J. Zool., Lond. (1999) 247, 257±268 # 1999 The Zoological Society of London Printed in the United Kingdom

The remarkable anatomy of the giraffe's neckN. Solounias
Department of Anatomy, New York College of Osteopathic Medicine of the New York Institute of Technology, Old Westbury, New York
11568-8000, U.S.A. E-mailL nsolounias@iris.nyit.edu(Accepted 19 June 1998)

Abstract
Mammalian cervical vertebrae 6 and 7 and thoracic vertebra 1 possess many distinguishing characteristics.
In the giraffe, bone morphology, muscle origins and insertions, as well as the location of the brachial
plexus (described as many osteological and some soft tissue characters) are identical to those in othermammals but are all displaced posteriorly by one vertebra. There are two exceptions to these observations:the pre-sacral vertebral count is unchanged when compared with that in the okapi and C7 supports the ®rst
rib. Thus, one vertebra has been added in the neck of the giraffe between cervical 2 and 6, and some type ofstructural blending has occurred in the region of the ®rst rib. The junction of the giraffe neck with thethorax is unusual and results in a protruding forelimb. It is possible that the unusual position of the neck
relates to balancing of a cantilevered neck and head upon a relatively slight body. Characteristic drinking
postures may have also in¯uenced the observed anatomical modi®cations.
Key words: neck anatomy, vertebral homology, giraffe, okapi

INTRODUCTION
It is well known that mammals typically possess sevencervical vertebrae. This number is stable from mouse towhale in contrast to the necks of reptiles and birds.
There are few exceptions to the number of seven cervicalvertebrae in mammals. The sloth Choloepus has a variable number of either six or seven cervical vertebrae.
The manatee Trichechus has six and the sloth Bradypus
has nine cervicals (Filler, 1986; Nowak, 1991). In contrast to the stability of the cervical vertebrae inmammals, the number of thoracic and lumbar vertebrae
is variable (Filler, 1986; Burke et al., 1995). Most
zoologists accept that the best example of stability in thenumber of cervical vertebrae in mammals is the giraffe
which has been observed to have seven. I propose toshow that the giraffe Giraffa camelopardalis has in a
subtle way escaped our scrutiny and actually has eightcervical vertebrae.
The junction of the neck with the thorax has always
been located at the occurrence of the ®rst rib on the ®rst
thoracic vertebra (T1) and on the location of the rootsof the brachial plexus, which relate the cervicothoracic
junction to the ribs and the arm (Burke et al., 1995;
Grif®n & Gillett, 1996). This junction de®nes which
region is thoracic and which is cervical. In addition,
there are clear anatomical differences between cervicaland thoracic vertebrae.

Previously, the morphology of the giraffe's neck waspoorly studied, although the physiology of pumping
blood high is well researched (Pedley, Brook &Seymour, 1996). The few systematic studies of Giraf®dae (e.g. Bohlin, 1926; Hamilton, 1978; Geraads, 1986)
did not consider the cervical vertebrae although theneck is a distinguishing feature of giraffes.
Lankester (1908) provided a brief osteological comparison of the cervicals of the giraffe and okapi Okapia
johnstoni in his study of the okapi, which is the only
other extant member of Giraf®dae; however, it is shortnecked. Lankester (1908: ®gs 64±71) focused thechanges in the shape of the articular facets (Appendix).
Commonly, there is a single pair of articular facets
between two vertebrae. Lankester (1908) observed that
there are articular facet changes in the okapi and thegiraffe as the cervical vertebrae are succeeded by thethoracic series. These changes are most apparent on theposterior aspect of C7 and the anterior aspect of T1 in
the okapi and may involve a facet splitting into two
separate parts: the traditional part is located morelaterally and the new facets more medially. These new
medially located split facets were termed accessory
articular facets, although sometimes they were not split
entirely from the original facet and were described as
con¯uent. The basic morphological feature of an accessory or a con¯uent accessory facet was a change inorientation from the primary articular facet. Unlike in258

N. Solounias

Table 1. Key morphologic characteristics of vertebra 6
Vertebral numbera
Characteristic

C6
Okapi and other ruminants

V6
Giraffe

Ventral tubercle
Ventral lamina
Transverse process
Length of transverse process
Shape of lateral wall of transverse process; costal element

AbsentPresent
Projecting
Short
Ridge with three protrusions

Present
Absent or modi®ed
Flat
Long
Not clearly formedaCounting from atlas as cervical number 1.

Table 2. Key morphologic characteristics of vertebra 7
Vertebral numbera
Characteristic

C7
Okapi and other ruminants

V7
Giraffe

Ventral tubercle
Pillar with anterior articular facets
Foramen transversarium
Transverse process
Transverse process
Shape of lateral wall of transverse process

AbsentWide and large
AbsentCon®ned
Projecting with three central costal protrusions
Large and triangular

Present
ReducedPresent
Continuous
Flat, costal elements are posteriorly
Elongate ridgeaCounting from atlas as cervical number 1.

the okapi where these facets were situated between C7
and T1, in the giraffe these facet changes take place one
vertebra back. In the okapi, these accessory facets occur
on the posteromedial surface of the lamina (arcus
vertebrae or lamina vertebrae) of C7 and join thecorresponding anteromedial surface of T1. In the
giraffe, they occur on the posteromedial surface of thelamina of the ®rst thoracic vertebra and join the corresponding anteromedial surface of the second thoracic
vertebra (Lankester, 1908: ®gs 64 and 67, respectively).
In summary, Lankester showed that accessory or con¯uent accessory facets occur between C7 and T1 in theokapi and between T1 and T2 in the giraffe.
In the same study, Lankester correctly pointed outthat the giraffe C7 and T1 are `cervicalized' (that is, they
resemble more anterior cervical vertebrae). Lankester
came close to recognizing that the presumed giraffe T1
is homologous to the actual C7 of other mammals ± thethesis of the present study, but did not. In this paper, I
discuss the structure of the vertebrae, muscles, andbrachial plexus and interpret the homology of thegiraffe's 8th vertebra. The easiest way to follow myreasoning is to ignore vertebral numbers in favour of
their morphology: e.g. C7 or T1 are structural entities
rather than bones assigned a number.
MATERIALS AND METHODS
The cervicothoracic osteology of many extant andextinct ruminants, including the modern giraffe andokapi, were studied. Particular attention was paid to thefossil vertebrae of fossil Giraf®dae such as Palaeotragus
primaevus from Fort Ternan (Kenya), Samotherium
from the Miocene of Samos (Greece), Palaeotragus
from Moldavia, and Sivatherium from the PlioPleistocene of the Siwaliks (India). Dissections of thecervicothoracic region were performed on white taildeer Odocoileus virginianus, goat Capra hircus, giraffeand okapi. In the present study, the symbol V is used
for the giraffe vertebrae instead of the traditional C or T
terminology (cervical or thoracic, respectively). For
example, C3 is V3, C7 is V7, and T1 is V8. In Figs 1, 2
and 3 the character with a number in a square meansthat it is in some way different from traditional
character in the giraffe.
The terminology of vertebrae and muscles used is as
in standard human and veterinary anatomy books (e.g.
Evans & Christensen, 1979; Nickel, Schummer &Seiferle, 1986: ®gs 28±48). The Appendix lists andclari®es certain anatomical terms used.
DESCRIPTION AND RESULTS
The characteristic morphology of the atlas (C1) and theaxis (C2) in mammals has been recognized for a longtime. Their special form has been related to the movements and support of the head. The distinctiveness ofthe mammalian C6, C7, and T1 has been underestimated however; each of these three vertebrae also has aunique morphology that can be readily recognized. In
contrast, cervicals C3±C5 are similar to each other andmay be considered to form a repetitive series.

Neck vertebrae of the giraffe

259

Table 3. Key comparisons of pairs of vertebrae; compare pair A, pair B, and C
Species

Proposed homology pairs
Vertebra number counting downfrom atlas as number 1
Proposed nomenclature
Current nomenclature
Rib
Position of spinous process
Verticality of spinous process
Pars interarticularis
Vertebral width at the anterior
facets in dorsal view
Vertebral width at the posterior
articular facets in relation tothat at the anterior facets

Okapi and otherruminants

Giraffe

Okapi and otherruminants

Giraffe

9 of okapi
10 of giraffe

A
Vertebra 7

A
Vertebra 8

B
Vertebra 8

B
Vertebra 9

Cvertebrae 9 and 10

C7
C7
AbsentAnterior
Inclined
With ridge
Wide

C7
T1
Present
Anterior
Inclined
With ridge
Wide

T1
T1
Present
Posterior
VerticalNo ridge
Wide

T1
T2
Present
Posterior
VerticalNo ridge
Wide-narrow

T2 and T2
T3 and T4
Present
Posterior
VerticalNo ridge
Narrow

Similar and wide

Subequal

Subequal

Subequal

Similar and narrow

Table 4. Key comparisons of pairs of vertebrae; compare pair A, pair B, and C
Species

Proposed homology pairs
Vertebra number counting downfrom atlas as number 1
Proposed nomenclature
Current nomenclature
Rib
Position of spinous process
Verticality of spinous process
Pars interarticularis
Vertebral width at the anterior
facets in dorsal view
Vertebral width at the posterior
articular facets in relation tothat at the anterior facets
Shape of articular area for theanterior facet
Location of anterior articular facet on
Transverse process: size andhorizontality
Distinction of pillar fromtransverse process
Orientation of pillar between
transverse process and anterior
articular facet
Size of pillar or degree of bone®lling of the lateral wall of thetransverse process and theanterior articular facet
Posterior ridge of pillar (between
transverse process and anterior
articular facet)
Shape of lateral wall of transverse
process
Length of vertebral body in relation
to that of vertebrae 9 and 10
Anterior region of vertebral body
Orientation of posterior articular facets
Accessory posterior facet
Orientation of anterior articular facets
Accessory anterior facet
Position of posterior articular facets inrelation to the anterior facets inlateral viewaOkapi and otherruminants

Giraffe

Okapi and otherruminants

Giraffe

9 of okapi
10 of giraffe

A
V7

A
V8

B
V8

B
V9

C
V 9 and V10

C7
C7
AbsentAnterior
Inclined
With ridge
Wide

C7
T1
Present
Anterior
Inclined
With ridge
Wide

T1
T1
Present
Posterior
VerticalNo ridge
Wide

T1
T2
Present
Posterior
VerticalNo ridge
Wide-narrow

T2 and T2
T3 and T4
Present
Posterior
VerticalNo ridge
Narrow

Similar and wide

Subequal

Subequal

Subequal

Similar and narrow

Round

Round

Round

Double faceted

Oval

PillarLarge and horizontal

PillarLarge andhorizontal
Distinct

PillarSmall

Pillar and lamina On lamina
Small
Small

Less distinct

Less distinct

Not distinct

Inclined anteriorly

Inclined
anteriorly

Slightly inclined

VerticalVerticalHollowed

Hollowed

FilledFilledFilledAbsentAbsentPresent

Present

Present

Large, with anterior,posterior, anddorsal processes
Long

Large, with
Large, with a
Small, noanterior,
dorsal processprocesses
posterior, anddorsal processes
Long
Short
Short

Short

ConvexLaterala
AbsentaMedialAbsentSame level

ConvexLateral-medial
Present
MedialAbsentSame level

FlattenedMedial-ventral
Absentlateral-dorsal
AbsentPosterior higher

Distinct

In some okapi individuals the accessory facets are present.

FlattenedMedial-inferior
AbsentMedialAbsentPosterior higher

FlattenedMedial-inferior
AbsentMedial-lateral
Present
Posterior higher

Small, one
dorsal conicalprocess

260

N. Solounias

C6

9

2

45a

1

V6

43
42

9

41

V7

43

9

44

45b

Fig. 1. Left lateral views. C6 of the okapi compared with V6and V7 of the giraffe.
Description of the various morphological conditions includedin Figs 1±3: Okapi C6: 1, ventral lamina of C6; 2, posterior
opening of the ®rst foramen transversarium which marks the
beginning of where the vertebral artery enters the cervicalvertebrae. Okapi C7: 3, the anterior positioning of the spinous
process of C7 of the okapi; 4, the anterior inclination of the
spinous process; 5, the pars interarticularis has a well de®nedridge; 6, the vertebral width posteriorly across the posterior
articular facets is similar to the width anteriorly forming a
rectangular outline in dorsal view; 7, the anterior articular
facet is located on a thin pillar of bone which is wide; 8, thetransverse process protrudes laterally and is similar to that of
C6; 9, the pillar is distinct from the transverse process andinclined anteriorly; 10, this pillar has no ridge posteriorly ± inthe giraffe, V8 should have a ridge if it were a true T1; 11, thetransverse process has three protrusions (a, b, c) which are thecostal elements ± in the giraffe V8, element 11b is notdistinguishable as a fully functional rib attaches there; 12, thelength of the vertebral body is intermediate between that of C6
and T1; 13, the anterior aspect of the vertebral body is strongly
convex; 14, the posterior articular facets face laterally; 15, theorientation of the anterior articular facets is medial. The
thoracic features of C7 are: 16, no foramen transversarium ±in the giraffe, V8 does not possess a foramen transversarium
since it is proposed to be a true C7; 17, C7 has no ventral
tubercle ± in the giraffe, V7 possesses a ventral tubercle unlike
the okapi C7. Okapi T1: 18, the attachment of the ®rst rib on
the anterior aspect of the vertebral body; 19, spinous process
situated posteriorly (overhanging) on the lamina; 20, spinous
process not inclined anteriorly; 21, pars interarticularis
without a lateral ridge (spinous process fades directly onto thepedicle); 22, the anterior articular facets are widely positioned;
23, the posterior articular facets are narrowly positioned; 24,
the posterior articular facets are located on the inferior medial
margin of the lamina directly under the overhanging spinous
process; 25, the pillar of T1 is unique in being massive andlong; 26, the pillar of T1 displays a characteristic posteriorridge; 27, the transverse process does not protrude laterally as
much as in C6 and C7; 28, the T1 pillar is not distinct form thetransverse process; 29, there are two costal protrusions on thetransverse process since a fully normal rib is attached on T1;
30, the vertebral body is shorter than in C7 but longer thanT2; 31, the anterior articular surface of the vertebral body is¯atter; 32, the orientation of the anterior articular facets issuperomedial; 33, the orientation of the posterior articular
facets is inferomedial. Okapi T2: 34, the ®rst vertebra with ashorter vertebral body; 25±36 all articular facets are locatedmedially; 37, short pillar; 38, deep groove on base of pillar; 39,
no sharp ridge on posterior side of pillar; 40, one costal
element on the pillar. Special features of the giraffe: 41, V6 has
no ventral lamina unlike a true C6; 42, transverse process does
not protrude unlike the true C6 cervicals of other ruminants;
43, V6 does not possess the ®rst foramen transversarium (V7
has an additional foramen transversarium with the vertebral
artery passing through it); 44, V7 has a normal ventral tubercle
unlike a true C7; 45a, the transverse process of C7 extends
laterally; 45b, the transverse process of V7 does not extend
laterally unlike a true C7; 46, in the giraffe, the facet for theattachment of the ®rst rib (cranial costal fovea) is unlike anyother mammal's as it forms an isolated island on the vertebral
body. The traditional facet is part of the anterior articulating
surface of the vertebral body (centrum).

Neck vertebrae of the giraffe
Vertebral morphology of C6±T2 in the okapi as a typicalungulate
It is necessary to describe some of the soft anatomy andosteology of the okapi's neck because it is the only otherextant giraf®d. All characters described for the okapi,
however, also represent characteristic and typicalmorphologies in most mammals (Tables 1±4).
C6 is the central region for the development of longus
colli muscles (musculus longus colli) which have threezones: cervical, transitional at C6, and thoracic. The
ventral surfaces of the vertebral bodies (centra) of C2±
C5 have midline ridges (cristae ventrales). This crista
ventralis separates the left and right portions of thecervical zone of longus colli muscle as they ascend
toward the anterior regions of the neck. The thoracic
portions of longus colli muscle pass posteriorly as far as
T5 but do not induce cristae ventrales at their attachments. The thoracic ®bres are longer than the cervical®bres and are not as deeply inserted on vertebrae C7±
T5. A crista ventralis is not well developed on C6
because the transitional longus colli is rhomboidal inventral view and connects the other two zones.
The C6 of the okapi has typical ventral laminae(Table 1; Fig. 1, C6, 1), which comprise a pair of large
plates of bone on the ventrolateral sides of C6 forming a
mid-line trough. In contrast, okapi C3±C5 do not havepaired ventral laminae but anteriorly on each vertebra
there are paired ventral tubercles representing reduced
laminae. The longus capitis muscle originates on theanterior part of the ventral laminae of C6. The thoracic
zone of longus colli muscle and scalenes muscles
originate on the posterior region of the ventral laminae
of C6. The scalenes directly connect cervical vertebrae
to ribs and their origins, insertions, and number isvariable in mammals. Most scalenes however, originate
on the posterior part of lamina ventralis of C6. The¯oor of the midline trough has no crista ventralis andthe transitional zone of longus colli muscles lies between
the left and right laminae. The transverse process of C6
protrudes horizontally and laterally. In contrast, thetransverse processes of C3±C5 do not protrude laterally.
The vertebral artery enters the foramen transversariumor costotransverse canal of C6 and then passes craniallythrough the other ®ve foramina transversaria. C6 is themost posterior (caudal) vertebra in which the vertebral
artery enters the foramen transversarium in most placental mammals (Fig. 1, C6, 2).
The following morphologic features of the okapi C7
also occur in C3±C6 and are important in evaluating thedegree of similarity of C7 to other cervicals and thedistinction of C7 from anterior thoracic vertebrae suchas T1. As in other cervicals, the spinous process of C7 of
the okapi is situated anteriorly and is inclined anteriorly(Table 3; Fig. 2, C7, 4). In addition, the pars interarticularis has a well-de®ned lateral ridge (Fig. 2, C7, 5)(Appendix). The vertebral widths posteriorly across the
traditional posterior articular facets or postzygoapophyses of cervical vertebrae (not the accessory) are
subequal or as wide across as the anterior articular

261

facets or prezygoapophyses and give a rectangulardorsal outline to C7 and to other cervical vertebrae(Fig. 3, C7). From C3 through C7 the anterior articular
facets face dorsally and medially and the posterior facelaterally and ventrally.
I term `pillar' the area of bone connecting the anterior
articular facet to the transverse process. The pillar in
cervicals is actually the anterior region of the vertebral
pedicle which extends to form the superior and posterior
margins of the intervertebral canal (Appendix). The
thoracic pillar is the region connecting the anterior
articular facet to the costal facet for the costal tubercle.
Cervical pillars have a characteristic shape; they are ¯atwhen compared with thoracic ones due to vertebral
elongation and an absence of ribs (Fig. 1, C7, 9; Fig. 2,
C7, 9). The thoracic pillars are situated laterally on the
superior margin of the transverse processes. The C7
pillar is ¯at and broad and has no ridge posteriorly
unlike the pillar of T1. In C7, the anterior articularsurface of the vertebral body is strongly convex. The
posterior articular facets of C7 face laterally and theanterior articular facets medially. In addition, C7 has no
foramen transversarium for the vertebral artery. Some
C7 vertebrae of the okapi and other ruminants possessvariably positioned foramina where a foramen transversarium would be located but dissections have con®rmedthat these are only venous. Any C7 foramina transversaria are usually small and asymmetrical, i.e. on only
one side, and often are located more dorsally on thepedicle than is a true foramen transversarium. Thus, inlateral view, they do not line up with the other foraminatransversaria of C3±C6. The ®nal feature is a character
in which C7 resembles a thoracic vertebra. C7 does notpossess a ventral tubercle in any mammal. Ventral
tubercles can be found on all C3±C5. C6 has anextended a ventral tubercle where special muscles attach
and which has been termed a ventral lamina (see above).
Thoracic vertebrae possess spinous processes that arevertical (relatively to the spinous process of C6 and C7)
and are situated more posteriorly so as to overhang overthe intervertebral foramina (Fig. 2, T1, T2). T1 (Tables
3 & 4; Figs 2 & 3) is a transitional vertebra between thewide cervical vertebrae and the narrow thoracics. Thus,
it has wide anterior articular facets and narrow posterior articular facets. The anterior articular facets of T1
face superiorly and medially as in cervical anterior
facets. They articulate with the posterior articular facetsof C7, which face laterally and ventrally. The T1
posterior articular facets, however, are located ventral
to the medial margin of the vertebral lamina or dorsal
table directly below the overhanging spinous process as
in other thoracic posterior articular facets. T1 is the ®rst
vertebra with posterior articular facets below the overhanging spinous process. The pars interarticularis of T1
has no lateral ridge (Fig. 2, T1, 21). Thus, there is asmooth concave and continuous surface connecting thebase of the spinous process to the lamina. The T1 pillar
is unique in being massive and long with a well-de®ned
posterior ridge (Fig. 2, T1, 25 and 26). This massivenessis a feature of thoracic pillars. The posterior ridge and

262

C7

T1

T2
20

4

3
19

5
15

14

21

32

24,33

10
17

39
40

36

26

16
9
13

33
35

37

25

27

11c

38

31

11a

29
28

11b

34

18
30

12

V8

V9

V10

46

Fig. 2. Left lateral views. Upper row C7, T1, and T2 of the okapi. Bottom row V8, V9, and V10 of the giraffe. For a description of the various morphologies see Fig. 1.

N. Solounias

8Neck vertebrae of the giraffe
C7

T1

6

22

T2

36
23

V8

V9

35

V10

263

with the wide rectangle of the cervical vertebrae. The
anterior facets of T2 face superolaterally. This orientation is totally reversed from that of all anterior articular
facets previous to T2 where the orientation was superomedial. The pillar of T2 is more vertically oriented and
it is short to that of T1. All thoracics posterior to T1
have short pillars.
The typical mammalian brachial plexus has ®ve
primary roots which exit anteroposteriorly about C7.
This is the situation in dogs Canis familiaris, goats
Capra hircus, and the white-tailed deer Odocoileus virginianus and is apparently the normal condition in allother mammals (Burke et al., 1995; Grif®n & Gillett,1996). The ®fth contribution between T2 and T3 is small
in the dog (Evans & Christensen, 1979: ®g. 17-2). In thedissected okapi only four roots were observed. The
main roots are normal and exit about C7. It is interesting that there are no roots that lie anterior to C7. The
two posterior roots appear normal and the most posterior is small and is between T1 and T2. There was noroot for the brachial plexus between T2 and T3 (Fig. 4,
top).
Vertebral morphology in the giraffe

Fig. 3. Dorsal views of juveniles. Upper row C7, T1, and T2of the okapi. Bottom row V8, V9, and V10 of the giraffe. Fora description of the various morphologies see Fig. 1.

the elongated pro®le, however, occur only on the pillarof T1 (Fig. 2, T1, 25 and 26). In summary, the T1 pillar
is unique and is unlike the thin pillar of C7 or the shortpillar of T2 both of which lack posterior ridges. The
anterior articular surface of the vertebral body is ¯atterin T1 and is the ®rst vertebra with a short body; bothare characteristics of thoracic vertebrae (Fig. 2, C7, 12
vs T1, 30). The ¯at articular surface is useful in locomotion by uniting effectively horizontal vertebrae. In
contrast, the convex surface on the vertebral bodies ofcervical vertebrae facilitates ¯exion of the neck.
T2 is the ®rst vertebra with both anterior and posterior articular facets located medially on the laminae(Fig. 3, T2). It is also the ®rst vertebra with anterior
facets located medially and directly anterior to thespinous process on the dorsal lamina. This is a drasticchange in position of the anterior articular facets fromlaterally on the pillars to medially and on the laminae.
This morphology correlates with the presence of ribs
which articulate by facets on the pillars and transverse
processes. Thus, the articular facets are positioned close
to the mid-line. In dorsal view, the four facets (twoanterior and two posterior) outline a narrow rectangle(Fig. 3, T2). This narrow rectangle strongly contrasts

The giraffe anatomy is remarkably similar to that of theokapi and other ungulates. This similarity is basic to thepresent argument for the presence of an additional
cervical vertebra. The similarity of vertebrae and surrounding soft anatomy supports the premise that
nothing has really changed in the details of the vertebrae, muscles and nerves in the giraffe, despite
elongation of the vertebrae. However, in all details theanatomical characters are located one vertebra posteriorly from where they should be (Tables 3 & 4). Even
the accessory facets occur one vertebra posteriorly fromthose of the okapi. Thus, C7 is located in the position of
T1, which is here termed V8.
V6 is unusual and is unlike a typical C6 which has thecharacteristic ventral lamina (Fig. 4). V6 not only does
not have the ventral lamina or the protruding transverse
process, but it is similar to the repetitive series of V3±
V5. The rhomboidal structure of the transitional longus
colli muscle is not situated below V6 but further posteriorly, below V7. Similarly, the longus capitis muscle
originates on V7.
V7 (Fig. 1, V7) strongly differs from a typical C7 inevery character (Fig. 2, C7). V7 resembles a typical C6
in that it has a normal foramen transversarium containing the vertebral artery and a ventral tubercle which
can be interpreted as a component of a ventral lamina(Fig. 1, 43 and 44). The ventral aspect of V7 includes thetransitional part of the longus colli muscle and longus
capitis muscle as it would if it were a C6. The transitional longus colli muscle is located centrally on V7.
There are no well-de®ned osteological ventral laminae.
Instead, a strong ligamentous bridge is located in theposition of the ventral lamina. This bridge is also foundin other C6 vertebrae of other mammals, where it is thin

264

N. Solounias
C4
T3

T2

C5
C6

C7

T4

T1

V5

V10

V6

V9

V10

V11

V12

V7

V8

Fig. 4. Lateral views of vertebrae and schematic location of the brachial plexi. Upper row: C4 through T4 of the okapi. Bottom
row: V5 through V12 of the giraffe. The symbol V is used for the giraffe vertebrae instead of the traditional C or T terminology(cervical or thoracic respectively). For example, C3 is V3, C7 is V7, and T1 is V8. Wavy black arrow shows location of accessory
articular facets sensu Lankester (1908: ®gs 64±71). Hollow arrow shows steep inclination of vertebral body of C7 and V8. This
inclination is characteristic of the C7. Thus V8 resembles a C7 and not a T1. Thin dotted arrow shows the ®rst vertebra with a¯attened anterior articulation of the vertebral body and is taken here to represent the true T1. Solid black arrow shows major
region of insertion of thoracic longus colli muscles. Dark regions show articular surfaces for the heads of the ribs and tubercles.
Hatching shows thoracic pillars. The pillar of T1 is large and inclined. The basic nerves of the brachial plexi form around C7 andV8. In the okapi there is no anterior branch between C5 and C6 in the brachial plexus. In the giraffe the anterior branch is
between V6 and V7 and is small. In the giraffe there is only one posterior branch. Thus, in the okapi the brachial plexus issimpli®ed anteriorly and in the giraffe it is simpli®ed both anteriorly and posteriorly.

Neck vertebrae of the giraffeand occupies a periosteal position. This type of bridge
can also occur in other vertebrae. I interpret thisligamentous bridge and the ventral tubercle as relicts ofa reduced lamina. The longus capitis has the majority of
its origin on the anterior margin of this ligamentous
bridge as if it were a C6.
The adult giraffe V8 is very similar to the okapi C7,
and is completely unlike a typical T1 except for thepresence of a rib. V8 is unlike a T1 possessing a longvertebral body, a highly convex anterior articular facet,a ridge on the pars interarticularis of the dorsal lamina,an anteriorly inclined and spinous process, and a thin
¯at pillar, as in a C7 (Fig. 2, V8). The posterior articular
facets are not situated inferior to the spinous process
but laterally as in a C7. Even the transverse process
protrudes as in a typical C7 despite the presence of a rib.
In the giraffe V8, the rib does not affect the shape of thetransverse process, which still resembles that of a C7.
The ®rst rib attaches in a totally unusual way on V8. In
typical vertebrae the rib head meets a facet that is
con¯uent with the anterior articular surface of thevertebral body. In the giraffe, the articular facet of the®rst rib is isolated and well posterior to the anterior
articular surface of the vertebral body of V8 (Fig. 2, V8,46). Two characters distinguish the giraffe V8 from atypical C7: (a) the presence of a rib (Fig. 2, V8 bottomrow), and (b) the posterior articular facets are positioned slightly more closely than the anterior. In thisrespect V8 is unlike a typical C7 and reminiscent of T1.
Cervicals of giraffe juveniles are important in this study
because their bones have not been subjected to extreme
elongation. Thus, the shape of the juvenile V8 of thegiraffe is identical to that of an adult or juvenile C7 of
the okapi (Fig. 3, V8 vs C7). This is especially true forthe width of the posterior articular facets of V8 which
are constructed as in a normal C7. Other juvenile
ruminants with long and short necks also possess juvenile T1s with structures similar to those in adults. I haveobserved a series of giraffe specimens of different ages
and have determined that during growth there is anallometric change as the posterior articular facets of V8grow much less apart (vertebral width) than the anterior
ones. This differential growth alters slightly the shape of
V8 which begins as identical to a C7 and with age
changes to one which is slightly narrower posteriorly,
thus tending towards a T1 morphology.
Accessory articular facets occur between C7 and T1 ina few okapi individuals (Lankester, 1908). In the giraffe,
the accessory facets are always present but are locatedone vertebra posteriorly, as expected. They occur
between V8 and V9. This occurrence is in agreementwith the current proposal that V8 is homologous to C7.
V9 of the giraffe is identical to a typical T1 and unlike
any T2. Thus, V9 possesses the long massive pillar witha well-de®ned posterior ridge as in typical T1s (Fig. 4,®rst grey region). The anterior articular facets arelocated laterally on the pillars and face medially as intypical T1s. Similarly, the pillars and articular facets of
V10 of the giraffe correspond to that of a typical T2.
Thus, the anterior articular facets are located for the265®rst time medially on the laminae as in all T2s (Fig. 3,
V10).
If V7 were the C7, the brachial plexus would exit
about V7, i.e. that is, one primary root anterior to V7
and the next primary root posterior to V7 as in theokapi (Fig. 4, top). The brachial plexus of the giraffe,
however, exits with V8 as a centre instead of V7, i.e. thetwo primary roots exit about V8. In the giraffe, there isone very small root anterior to V8 (between V6 and V7).
This root is absent in the okapi I dissected. Posterior toV8 there is only one more root between V9 and V10(Fig. 4, bottom). Thus, the giraffe brachial plexus ishighly concentrated.
In summary, the basic nerves of the brachial plexi
form around C7 in the okapi and V8 in the giraffe. In
the okapi there is no anterior branch in the brachial
plexus. In the giraffe the anterior branch is present, but
small, showing that in this aspect the giraffe is lessspecialized than the okapi. In the giraffe, however, there
is only one posterior branch which makes the giraffe
specialized in this aspect. Thus, in the okapi the brachial
plexus is simpli®ed anteriorly and in the giraffe it issimpli®ed both anteriorly and posteriorly. Using thebrachial plexus, the homology between C7 of the okapi
with V8 of the giraffe can be strengthened.
DISCUSSION
Lankester (1908) proposed that T1 of the giraffe iscervicalized. I consider it unlikely, that owing to thedetail of the change, V6, V7, V8 and V9 have changed
shape completely due to some function. It might beproposed that the observed morphology of V6±V8 in
the giraffe is due to the extreme elongation of the neck.
Examination of the long necks in other mammals,
however, shows that cervical vertebrae are morphologically typical with seven elongated vertebrae. I haveexamined llamas Lama glama and L. vicugna, camels
Camelus dromedarius and C. bactrianus, including theextinct camelid Aepycamelus, mohor gazelles Gazelladama, dibatags Ammodorcas clarkei, gerenuks Litocranius walleri, the litoptern Macrauchenia, as well as theextinct giraf®ds Samotherium and Palaeotragus(Godina, 1979). Thus, length alone may not have been a
directing force in the observed specializations of thegiraffe neck.
The junction of the neck with the thorax (the cervicothoracic junction) has always been based on two
characters that are coupled in mammals: the occurrenceof the ®rst rib and the location of a brachial plexus
centred on C7 (Burke et al., 1995; Grif®n & Gillett,1996). In the examples of lost vertebrae no dispute canbe posed. In the sloth Bradypus where there are ninecervicals, the cervicothoracic junction is still typical interms of the ®rst rib and the brachial plexus. The giraffe
is truly unusual in that the brachial plexus centres
around V8, the same vertebra which bears the ®rst rib.
It is proposed here that V8 is homologous with the C7of other mammals.

266

N. Solounias

Normal positionof glenohumeral
joint

(a)

(b)

Fig. 5. Lateral views of an actual giraffe (a) and an imaginary giraffe (b). The imaginary giraffe has a neck in the typicalruminant location. Note that the actual position of the glenohumeral joint for the giraffe is highly different from the typical
position in ungulates indicated here as (b).

It would be ideal if the giraffe had an extra vertebra
or rib in terms of total number but it does not (using theokapi as a standard). Both the giraffe and the okapi
have a total of 26 pre-sacral vertebrae and 14 pairs of
ribs. There is no apparent difference in the number ofthoracics ± de®ned as those which possess a rib ± or
lumbars. I have not observed sacralized lumbars orsacrals where an extra vertebra would hide. Thus, thegiraffe V8, although entirely a C7 in morphology,
eliminates one thoracic vertebra in the thorax by taking
its place. In terms of the ®rst rib and of total number,
V8 is the ®rst thoracic. In terms of morphology
however, V8 is a C7. Apparently morphogenetic
blending of vertebrae occurs at the cervicothoracic
junction.
The position of the giraffe neck on the thorax is also
unusual. The neck in most mammals enters the thorax
from the anterior direction and in front of the ®rst rib.
In the giraffe, the neck enters the thorax over thescapulae from an anterodorsal direction. In most quadrupedal mammals, the glenohumeral joint is locatedwell posterior to the manubriosternal angle in lateralview and between the ®rst and second ribs. In the giraffe
however, the glenohumeral joint is unique in that it
protrudes anteriorly to the manubrium and to the ®rst
rib. This posterior position of the neck in relation to theshoulder (glenohumeral joint) is a feature that distinguishes giraffes in photographs and in art (Fig. 5).
When giraffes drink water from a low source, they
commonly spread their forelimbs apart (downward
from the elbow). In that position, the proximal forelimbs, glenohumeral joints and scapulae approach the
midline of the body. In order for this approach to takeplace, the forelimbs must protrude in front of the thorax

unlike the limbs of typical ungulates. As they drink, theneck begins behind the closely approximated scapulaeand humeri and then runs dorsal to them. It appears
that if the neck were in the typical mammalian location,
the soft parts would be constricted between the approximated scapulae obstructing the wind pipe andoesophagus. It may therefore be possible that the neckhas been placed in this uncommon position so the
giraffe can breathe while drinking with its forelimbs
abducted.
In conclusion, the giraffe V6 is not homologous to
the C6 of other mammals. V7 is homologous to C6,
V8 to C7, V9 to T1, and V10 to T2. Data on juveniles
and all anatomical structures support this hypothesis.
There is no morphology that potentially violates thisobservation which is in agreement with theories ofhomology (e.g. Bock, 1989). Thus, an intercalated
cervical vertebra is present between V2 and V6 in the
giraffe. There are two unusual features in the giraffe:(1) that C7 (V8) has an articulating rib that has
obstructed the recognition of V8 as a true C7; and (2)that C7 plays a dual role morphologically as a cervicalbut also takes the place of vertebra number 8 in thethoracic region, resulting in a total count of vertebrae
equal to that of the okapi. Cervical vertebral additionand subtraction has occurred, albeit rarely, inmammals. Bradypus is the only mammal that has ninecervicals and demonstrates that it is possible for thegiraffe to have eight, although in the giraffe the ®rst
rib located on V8 masks its cervical nature. At present
it is not clear how or where exactly a vertebra isadded in the neck of the giraffe. What is almost
certain is that an insertion has taken place between C2and C6.

Neck vertebrae of the giraffe
SUMMARY
Each of the mammalian cervical vertebrae C6 and C7
and thoracic vertebra T1, possess several distinguishing
characteristics. In the giraffe, these three vertebrae andtheir associated soft tissues are identical to othermammals but are displaced posteriorly by one vertebral
position. Many morphological conditions (characters)
including vertebral morphology, longus colli and longus
capitis muscles and the con®guration of the roots of thebrachial plexus support this ®nding. Thus, the ®rst
thoracic of the giraffe (vertebra number 8) is morphologically equivalent to the seventh cervical vertebra, andthe second thoracic (vertebra number 9) is identical tothe ®rst thoracic of other mammals. V7 is homologous
to C6, V8 to C7, and V9 to T1. These observations
indicate that one vertebra has been added in the neck of
the giraffe between C2 and C6. The ®rst rib is unusualin articular position and in relation to surrounding
structures and attaches on C7 (vertebra number 8),
masking the recognition of the true C7. The position of
the giraffe neck is unusual as it attaches to the thorax
more posteriorly and superiorly than in typical necks.
As a result, the glenohumeral joint protrudes in lateralview giving the giraffe its characteristic silhouette.
Acknowledgements
I thank David Eliot for numerous discussions and forhis help with the dissections; Ed Heck for the art work;
Mike Douglas, Andy Bailey and the Memphis Zoo forproviding the body of a giraffe for dissection; Lowensteen and Sawyers at the San Diego ZoologicalSociety for providing okapi and young giraffe specimens; the Brookville Zoo and the Field Museum of
Natural History in Chicago for an okapi specimen; theAmerican Museum of Natural History for access to267

specimens; NYCOM for ®nancial support; and Juliet
Clutton-Brock, John Hunter, Ross MacPhee, Arnold
Nagler, Ann Patrick, Bill Stanley and Alan Walker forcomments and help.
REFERENCES
Bock, W. J. (1989). The homology concept: its philosophical andpractical methodology. Zool. Beitr. 32: 327±353.
Bohlin, B. (1926). Die Familie Giraf®dae. Palaeontologia Sinica,
Peking (C) 4: 1±178.
Burke, A. C., Nelson C. E., Morgan, B. A. & Tabin, C. (1995).
Hox genes and the evolution of vertebrate morphology. Development 121: 333±346.
Evans, H. E. & Christensen, G. C. (1979). Miller's anatomy of thedog. 2nd edn. Philadelphia: W. B. Saunders.
Filler, A. G. (1986). Axial character seriation in mammals. Ph.D.
thesis, Harvard University.
Geraads, D. (1986). Remarques sur la systeÂmatique et laphylogenie des Giraf®dae (Artiodactyla, Mammalia). Geobios
19: 465±477.
Godina, A. R. (1979). Historical development of the giraffes.
Acad. Stud. Soviet Union. 177: 1±103.
Grif®n, E. B. & Gillett, M. (1996). Neurological and osteologicalde®nition of mammals. Brain Behav. Evol. 47: 214±218.
Hamilton, W. R. (1978). Fossil giraffes from the Miocene of
Africa and a revision of the phylogeny of the Giraffoidea.
Philos. Trans. R. S. London B 283: 165±229.
Lankester, R. (1908). On certain points in the structure of thecervical vertebrae of the okapi and the giraffe. Proc. Zool. Soc.
Lond. 1908: 320±334.
Nickel, R., Schummer, A. & Seiferle, E. (1986). The anatomy ofdomestic animals, 2. Berlin and Hamburg: Verlag Paul PareySpringer.
Nowak R. M. (1991). Walker's mammals of the world. Baltimore,
MD: The Johns Hopkins University Press.
Pedley, T. J., Brook, B. S. & Seymour, R. S. (1996). Bloodpressure and ¯ow rate in the giraffe jugular vein. Philo. Trans.
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Williams P. L. (1995). Gray's anatomy. 38th edn. New York:
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Appendix. Anatomical clari®cations
The terminology of vertebrae and muscles used in thepresent study is in standard human and veterinary
anatomy books (Nickel et al., 1986: ®gs 28±48).
The base of the vertebral spinous process is termedlamina (arcus vertebrae or lamina vertebrae). This isdifferent from the ventral lamina (lamina ventralis)which is a morphologic feature of a C6. The ventral
lamina is an enlarged ventral tubercle (tuberculum
ventralis) which occurs in most cervical vertebrae.
Typical cervical vertebrae possess ventral and dorsal
tubercles. The dorsal tubercle is the posterior region of
the transverse process.
The pars interarticularis is de®ned as a strong lateralwall between the anterior and posterior articular facets.
It is the lateral edge of the lamina. This lateral wall issmooth in thoracic vertebrae but in cervicals it forms acharacteristic ridge; the edge. Other pars interarticlularisof vertebrae are not discussed in this study.
Commonly there is an anterior and a posterior pair ofarticular facets on the laminae. The accessory articular
facets are more medial than the traditional ones and are
facets which display different orientation from the traditional ones. Often they form a continuous articulating
surface with the traditional articular facets but they canbe distinguished by the drastic change in orientation.
Accessory facets occur between C7 and T1 of the okapi
and between V8 and V9 of the giraffe.
The new term `pillar' (pila) is the area of boneconnecting the anterior articular facet to the transverse
process. The pillar is part of other regions of thevertebra. It is a thicker and more elevated area of bonethan the pedicle proper posteriorly to it. The mostdorsal part of the pillar, immediately ventral to theanterior articular facet, has been termed paraprezygapophysis and diapophysis in human anatomy (Williams,
1995: ®g. 6.89). The most ventral part of the pillar is the
beginning of the transverse process. The anterior edgeof the pillar is the posterior half of an intervertebral
foramen. Cervical pillars have a characteristic shape:
they are ¯at when compared to thoracic ones due tovertebral elongation and an absence of ribs. The pillarof C7 is the widest. Thoracic pillar is the region connecting the anterior articular facet to the costal facet forthe costal tubercle of the rib. Thoracic pillars are
situated at the most lateral margin of the transverse
process (they protrude). The pillar of T1 is tall and has awell de®ned posterior ridge.
The foramen transversarium or costotransverse canalis the bony canal beginning with C6 through which thevertebral artery ascends. All cervicals have this canal inruminants except C7. The lateral wall of the canal isembryologically formed by the cervical costal process(reduced cervical ribs).
The intervertebral foramen forms between two articulated vertebrae. The spinal nerves and roots of brachial
plexi exit through these foramina.