NOTES ON THE FOETAL SKULL OF]}fESOPLODON STE]NEGERJ*CHARLES McCANN
8 Kiwi Street, Heretaunga, Upper Hutt, New Zealand

ABSTRACTThe cranial anatomy in the skull of a foetal Mesoplodon stejnegeri
True is described and illustrated. Some of the more important changes
which take place in the structures in the course of their developmentfrom the foetal to the adult state are discussed.
INTRODUCTION

The Ziphioid skull is, perhaps, the most asymmetrically distorted of all mammalian crania. In the adult some of the elements are partially or completely
overlaid, fused or so closely interdigitated that they defy separation and theirrelationship to one another is often most puzzling. In the advanced foetal
stage the bones fall apart readily, on maceration, and allow of a greater
understanding of the complex arrangement of the cranial components. However, it is seldom that a specimen, young enough, is available to study the
intricate anatomy of such a skull.
On the 28th September, 1937, the late Dr. W.R.B. Oliver collected a specimen of 1VIesoplodon stejnegeri True which stranded on the Waiterere Beach,near the Manawatu Heads (Dom. Mus. 619). The specimen, a female, contained
a full term foetus (Dom. Mus. 620, skeleton). The skeletons of both are preserved in the Dominion Museum, W ellin~ton.
In the flesh, the adult measured 4,200 mm (14 ft) in total length and the
foetus 1,550 mm (5ft 2 in). Mesoplodon stejnegeri is, perhaps, the smallest species
in the genus. As the neonatals of Mesoplodon are approximately one third
the length of the parent at birth, there seems little doubt that the adultpresumably came inshore to calve, when she met her death. Three species ot
Mesoplodon, JVI. grayi, M. layardi and M. stejnegeri, are known to calve in
New Zealand waters during the spring of the Southern Hemisphere.
Unfortunately, portions of the skull of the foetus have been lost or disintegrated during maceration; nevertheless, there is sufficient material available
worthy of description and comment. As most of the cranial elements havefallen apart along their sutures, description of the various components andtheir relationship to each other is made comparatively simple. I draw attention to the main features of the skull below.
* This paper was compiled during my service with the National Museum, Wellington.
Sci. Rep. Whales Res. Inst.,
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McCANN

ANATOMICAL OBSERVATIONSAt this early age the axial base of the cranium (basis crani) is composed ofthree separate masses: anteriorly, the vomer-presphenoid mass; mesially, thebasisphenoid mass; and, posteriorly, the basioccipital mass.

Vomer-presphenoid mass. (Pls. 3, fig. I ; Pl. 4, fig. 1)
Viewed dorsally, the rostral portion of the vomer (V) is a lanceolate channel or trough, deepest proximally (Pl. 3, figs. 1, 4). At the point of fusion
with the presphenoid (PS), a portion of the vomer is obscured by the superimposition of the presphenoid (PS) and the ethmoid, but the vomer reappears
posteriorly as a thin, horizontal, retuse, somewhat ligulate bone, the laterallobes of which are slightly depressed on either side of the mid-line (Pl. 3, fig.
4). Viewed laterally, the vomer is somewhat canoe-shaped with a short 'dropkeel' (K) near the middle of its length. Ventrally, the vomer is strongly keeled
except for the posterior, horizontal expansion. At the point of fusion between
the internal, lateral walls of the vomer, and the presphenoid, there is an articular surface for union with the pterygoid bone. On the interior wall of thepresphenoid are clearly seen the lines of fusion between it (presphenoid) andthe ethmoid. The ethmoid fuses also with the adjacent walls of the vomer,
but at this early age the base of the ethmoid is not in contact with the vomer
below; at a later stage of development the union is completed.
The presphenoid rises in a steep curve from its almost horizontal floor toform the fore part of the cranial cavity. It lies across the axial base of thevomer, but it is free from the vomerine channel at this period of development.
No foramina are apparent on the walls of the presphenoid, but a shallow
sulcus is formed on the lateral edges which eventually contribute to the formation of the optic f oramen and the fora men lacerum. The suture between
the presphenoid and the basisphenoid is filled with cartilage. In the adult,
although the suture narrows, the two bones never seem to fuse; there is always
a gap between them.
Proximally, the ethmoid is composed of rather spongy bone fusing withthe presphenoid and the vomer; anteriorly, it continues in the trough of thevomer (mesorostral groove) as the masorostral cartilage. With advancing age
this cartilage ossifies and fuses with the adjacent bones and, in adult males
completely fills the groove with dense, ivory-like bone; but in females theossification is net so marked, the groove is only partially filled with bone ofa more spongy nature (Pl. I, OC). Some authorities hold that the filling of
the mesorostral groove is effected by proliferation of the vomer itself (Forbes,
1893)*, but this view does not appear to be borne out by careful examinationof transverse sections of the rostrum.
*Forbes, H.O., 1893.

Proc. Looi. Soc. Lond. pp. 216-236, pls. 12-15.
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FOETAL SKULL OF MESOPLODON STE]NEGERI109

Basisphenoid mass. (Pl. 3, figs. 2, 12 ; Pl. 4, fig. 2)
Viewed dorsally, the basisphenoid (BS) is somewhat butterfly-shaped(Pl. 3, figs. 2, 12), with great 'pedunclate' wings (alisphenoid) outspread obliquely
forwards, the anterior margins of which articulate with the pterygoids. About
the middle of the body of the basisphenoid is a shallow depression (pituatary
fossa); on either side of this fossa is a large foramen (foramen ovale) (FO).
The foramina pass obliquely backwards to the exterior.
As already observed, the anterior articulation is imperfect mesially, but theantero-lateral edges articulate with the presphenoid. The posterior articularsurface of the basisphenoid is not markedly separated from the basioccipital. In
the adult this suture fuses completely, and this union between the basisphenoid
and the basioccipital becomes almost invisible. Ventrally, the basisphenoid isshallowly grooved, longitudinally (Pl. 3, fig. 12). Posteriorly, on either side of
the median groove, are the elevated articular surfaces which articulate with thebasioccipital crests or wings.
Basioccipital mass. (Pl. 3, fig. 3; Pl. 4, fig. 3)
Viewed dorsally, the surface of the basioccipital (BO) is somewhat
triangular; the articular surface of the basioccipital with the basisphenoid
is marked by four scallops (Pl. 3, fig. 3; Pl. 4, fig. 3); mesially there is ashallow fossa on either side of which there are articular surfaces for theadjacent bones. Posteriorly, a rounded projection forms the lower margin ofthe· fora1nen magnum between the bases of the occipital condyles. Laterally,
the basioccipital crests fall away obliquely with forwardly directed projections
articulating beneath the basisphenoid. Postero-laterally, the basioccipital crests
articulate with the exoccipitals.
With advancing age, the basisphenoid is 'crushed' between the presphenoid
and the basioccipital, and, eventually, it (basisphenoid) fuses completely withthe latter bone. The alisphenoids appear as irregularly shaped bones on theexterior of the skull, adjacent to the squamosal. The posterior horizontal
portion of the vomer overlies the greater part of the basisphenoid and a portionof the basioccipital subsequently fusing with them.
Maxilla. (Pl 3, figs. 5, 6; Pl. 4, fig. 14)
Adpressed to the lateral portion of the vomer is the lanceolate projectionof the maxilla (MX) ; posteriorly, the maxilla flattens out almost horizontally
to form a broad supra-orbital expansion as in the adult (Pl. 3, fig. 6). Itsposterior margin bends round towards the mid-line of the skull and contributes
to the formation of the vertex and the lambdoidal ridge. In the foetus, abasirostral groove (DN) is present, extending from below the maxillary tubercle
to the anterior extremity, just below the dorsal profile of the maxilla. This
groove is believed to be homologous with the dentary groove of othermammals. This canal apparently houses the dentary branch of the superior
maxillary nerve. In the adult of Mesoplodon stejnegeri the basirostral groove
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McCANN(BG) is absent, being completely filled with secondary bone. In. some species
this grove is present throughout life (M. grayi) and forms a useful accessory
character in diagnosis of the species.
The dorsal profile of the rostral portion of the maxilla slopes gently
upwards towards the nares (NR) ; the lower is almost straight, rising abruptly(at an angle of about 45 degrees) at a vertical dropped at the maxillary
tubercle (MT). The cranial portion of the maxilla is expanded laterally, as
already indicated above, but does not margin the orbit. The inner face ofthe maxilla is sculptured to articulate with the premaxilla and the vomer.
The outer face is sculptured posteriorly to articulate with the palatine bone(PL), (Pl. 3, figs. 5, 6). From above, on the inner side of the maxillary
tubercle, the large maxillary foramen (MXF) is visible. Another large foramen(sometimes additional secondary foramina are present), the post-maxillary
foramen (PMXF), is to be seen near the middle of the flattened expansion or'maxillary plate'. The expanded portion of the maxilla over-rides the malarbone (jugal}, the lachrymal bone and the frontal bone (F), except for its(frontal) lateral margin which forms the orbit.

Premaxilla. (Pl. 4, figs. 13)
The premaxilla (PMX) is a much elongated, compressed and twisted bone,anteriorly wedged between the vomer and the maxilla and posteriorly margining the anterior nares (NR) and forming part of the vertex. Its posterior
extremity forms part of the 'hood' over the anterior nares (the hood is mostpronounced in M. stejnegeri).
Dorsally, the premaxilla is perforated by the premaxillary foramen (PMF).
In the foetus the premaxillary foramina are approximately on· the sametransverse level as the maxillary foramina, but with the elongation of therostral bones, the premaxillary foramina mores a short distance behind themaxillary foramina as in the adult. A canal, carrying a branch of thetrigeminal nerve and the associated blood vessels, enters the matrix of thepremaxilla and travels to its anterior extremity. This canal is connected withthe premaxillary foramen. The dorsal margin of the premaxilla, together withthe wall of the vomer, encloses the mesorostal cartilage, but the premaxilla
exceeds the vomer in length, and, anteriorly, the premaxillae alone constitutethe groove. In the adult the bone of the premaxilla is much denser than thatof the maxilla.
Palatine bone (PL). (Pl. 3, figs. 5, 6; Pl. 4, fig. 15)
The palatine bone is sandwiched between the maxilla and the pterygoid
and when the latter bone is in place the major portion of the palatine isobstrucured, with only a narrow margin of its anterior extremity anddorsal edge margining the pterygoid above. Anteriorly, the palatine bone issomewhat arrow-headed in shape (Pl. 3, fig. 5, 6 (PL)). Postero-dorsally, two
short articular surfaces project, the upper in contact with the maxilla, frontal
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111

and the lachrymal bones; the lower, with the lachrymal alone. Posteroventrally, the palatine bends round the angle of the maxilla forming a small
lobe compressed between the maxilla and the vomer. The external face of thepalatine articulates with the pterygoid and eventually fuses with it completely.
A portion of the palatine enters the anterior nares.

Pterygoid bone (PY). (Pl. 3, figs. 1, 8; Pl. 4, fig. 16)
The pterygoid bone is somewhat triangular in general shape. Posterodorsally the pterygoid articulates with the vomer and the base of thepresphenoid and, in time, fuses with them; its internal lateral face abuts theexterior of the palatine bone and eventually fuses with it. Externally, thepterygoid is concaved and forms what is known as the mesial lamina (PML);
its lower margin turns outwards and posteriorly forms the pterygoid hamulus(H). Together the paired pterygoids form the posterior nares which contains
the laryngeal mass. The pterygoids approximate each other along the axial
line but, normally, do not fuse with each other, even in the adult.
Lachrymal bone (L). (Pl. 3, figs. 11 a, 11 b ; Pl. 4, fig. 12)
The lachrymal bone is roughly oblong in shape. Viewed ventrally, theanterior half is flat, but the posterior half presents a strong keel. Dorsally, it
is in contact with the maxilla and the anterior portion of the frontal, forming
the orbital margin. Posteriorly, it is also in contact with the palatine andwith the pterygoid. Anteriorly it is in contact with the malar bone. (Pl. 3,
figs. lla, llb)
Malar bone (Jugal).
The malar bone is missing in the specimen under discussion. In the adult,
the malar is a flattish, triangular bone giving off, posteriorly, the slenderzygomatic process; it is in contact with the maxilla internally and with thelachrymal externally. Anteriorly, it borders the antorbital notch.
Together with the lachrymal, and the anterior extrenity of the frontal
forming the orbit, the malar contributes to the formation of the antorbital
tubercle.
Frontal bone (F). (Pl. 4, figs. 9, 11 ).
Dorsally, the frontal bone (F) is almost completely overlaid by the
expansion of the maxilla, but, laterally, it borders the maxilla and contributes
to the foramation of the orbital-the lateral border of the frontal forms thesuperior border of the orbit. Anteriorly, its extremity interlocks between the
maxilla and the lachrymal; posteriorly, the orbital ridge terminates in a free
process above the squamosal. Posteriorly, the edge of the frontal can befollowed, wedged between the maxilla and the supraoccipital, and thence
twisting round into the vertex of which it forms part, under the maxillary'plate'. Its posterior wall forms part of the brain case.
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McCANN

Nasal bone (N). (Pl. 4, fig. 10)
The nasal bone (N) are paired. Each bone is somewhat cuboidal in shape(Pl. 4, fig. 10) in the foetus; they are 'free'-they drop out of position onmaceration. In the adult the nasals lose some of their shape and become
welded to the adjacent bones posterially and laterally; anteriorly they are
free, and contribute to the formation of the anterior nares. In the foetus thetwo nasals are in contact with each other mesially, but not fused; laterally
the bones are adpressed to the internal faces of the premaxillae; ventrally
they are in contact with the mesethmoid.
Narial passage (NR).
The narial passage is divided into two by a septum formed largely by
the vomer and the ethmoid. The recurved walls of the vomer, together witha portion of the pterygoids, compose its posterior wall; the lateral walls areformed largely by the pterygoids and small segments of the maxillae andpalatines; and, the anterior wall, partly by portions of the premaxillae, maxillae
and pterygoids. The superior wall of the posterior passage is formed largelyby the horizontal, posterior expansion of the vomer and a small segment of
the frontals. The inferior walls are formed by the pterygoids.
A large foramen perforates each of the lateral walls of the anterior nares,
carrying a branch of the trigeminal nerve and the associated blood vessels.
Interparietal (IP). (Pl. 3, figs. 9a, 8b, 9e, 10; Pl. 4, fig. 4)
The interparietal is a dense obovoid bone with a ventral keel which fuseswith the falx cerebri. Anteriorly, it is in contact with the frontals; laterally
and posteriorly it fuses with the adjacent bones and with age loses its identity
as a separate element. In the foetal specimen its sutures are still visible onits ventral aspect.
Parietals.
The parietals are damaged beyond recognition m the specimen.
Siipra-occipital SO. (Pl. 4, fig. 4)
The suppraoccipital at this early stage is very fragile. It is domed, witha median depression exteriorly; interiorly a deep flange forms part of thefalx cerebri. At the posterior end of the falx cerebri is the internal occipital
protuberance.
Exoccipital (EO). (Pl. 4, fig. 5)
The exoceipital is somewhat squarish. The superior margin fuses withthe supraoccipital eventually; ventrally it articulates with the posterior marginof the basioccipital crest and, eventually, fuses with it; its lateral margin
articulates with the squamosal and fuses with it; at its inner angle is theoccipital condyle. Between the lateral margin and the condyle there is a deep
notch along its ventral border ; within this notch there is the exist leading
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113

outward from the internal condylar foramen. The fusion of the exoccipitalwith the basioccipital is so complete in the adult that it appears as though
the exit foramen was situated between the two bones.

Squaniosal bone (SQ).
The squamosal bones (SQ) have been lost in the foetal specimen.
portion of one is preserved but is insufficient for description.

A

Mastoicl process.
A mastoid process arises from the posterior of the auditory bulla andinterdigitates with the posterior protuberance of the squamosal; it is connectedto the bulla by a narrow neck. On its latero-ventral surface is an articularface which articulates with a corresponding surface on the posterior lobe of
the periotic bone. (Pl. 4, fig. 8).
Tympanics.
Viewed ventrally, it will be seen that the bulla (B) (Pl. 4, fig. 6) obscuresmuch, if not all (all in adult) of the periotic bone (Pl. 4, fig. 7) lying beneathit. The two bones are connected to one another by a thin, fragile piece ofbone. The eustachian canal opening is directed forward. Externally, theventral surface of the bulla is divided into two lobes, an internal lobe runningparallel with the basioccipital crest and an outer, smaller lobe.
The periotic bone (Pl. 4, fig. 4), perhaps, the most solid in the wholeskeleton (of cetacea), fits closely into a hollow formed in the squamosal. Anteriorly, the periotic is margined by a thin falciform process, arising from thesquamosal. The periotic bone may be divided into three regions; an anterior
lobe with an articular face for the margin of the eustachian tube, a central
lobe perforated by several foramina and a posterior lobe with an articularsurface to receive the counter part of the bulla already referred to.
Manclibles (MN). (Pl. 4, fig. 17)
The mandibles at this early age are very fragile. Along the superior
margin the dentary groove is completely open. Near the posterior union of
the symphysis a single mandibular tooth is present in each ramus. The tooth
is just a hollow triangular shell with an acute tip. (Pl. 4, fig. 17). On theexterior face of each ramus, in the vicinity of the tooth, there are the mental
foramina. The posterior blade of the ramus is about twice as deep as theanterior; the coronoid is slightly anterior to the articular condyle and, theangular slightly posterior to it.
Course of the 5th cranial nerve (trifacial). (Pl. 5)
The course of the 5th cranial nerve in Mesoplodon calls for some comment
because of the great departure of the cranial elements from the more familiar
mammalian type of skull. Because of the distortion that takes place, it isdifficult to correlate the various branches with the ramifications of theSci. Rep, Whales Res. Inst.,
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McCANNcorresponding nerves observed in other mammals, including .Man. The exit
foramina of some of the major branches play an important role in taxonomic
description.
The courses of the nerves and the associated blood vessels are represented
in the skull by canals and these have been traced by means of wire tracers.
In the foetus of 1VIesoplodon stejnegeri, as with other mammals, the 5th
cranial nerve leaves the brain case through the foramen lacerum and entersa large cavity (homologous to Meckel's cavity in Man) situated just below themaxillary foramen (MF). Within the cavity lies a large ganglion, Gasserian
Ganglion, which gives off several branches to the facial region. Posteroventrally, a short branch perforates the lateral wall of the anterior nares (NR)tnrough the maxilla ('Nasal' branch). Postero-dorsally, another large branch
is given off which courses backwards, partly through the maxilla and partly
between the maxillary and frontal 'plates', and emerges to the exterior of theskull through the post-maxillary foramen (PMXF). This branch probably
corresponds to the frontal branch (of human anatomy).
Antero-dorsally, two closely associated branches are given off, the larger
emerging to the surface through the maxillary foramen (MF) the smaller,
passing under a bony ridge, crosses the suture between the maxilla andpremaxilla and, finally energes through the premaxillary foramen to the dorsal
surface of the skull.
Below the maxillary foramen a large branch from the ganglion courses
forwards the full length of the maxilla, just below its superior margin, in an
open channel. This branch is the homologue of the dentary nerve (DN) inother mammals. The bony channel is referred to, in cetacean parlance, as
the basirostral groove. The presence (in 1\!I. grayi and 1\!I. bidens) or absencein 1\!I. layardi and others) of the basirostral groove in 1\!Iesoplodon is of somediagnostic value when describing or determining adult skulls and it has been
made use of. In the adult skull of 1\!I. stejnegeri the basirostral groove (BG)
is absent but in the foetal skull the groove is present. (Reference to thedisappearance of the groove in the adult will be discussed below).
From below the premaxillary foramen, a branch leaves the ganglion andcourses forwards, at first through the matrix of the premaxilla and then along
the suture between the premaxilla and the maxilla, to the extremity of therostrum. The canal for this nerve is readily seen in a cross section of therostrum (PN).
Below the dentary branch (DN) another large division leaves the ganglion,
at first descending between the maxilla and the palatine bone, then, entering
the matrix of the maxilla at about the middle of its depth, it descends
gradually to the inferior margin of the maxilla where it emerges by a foramensome distance short of the extremity of the maxilla (median maxillary nerveMMN). Yet another large nerve leaves the ganglion and after coursing
forwards through the matrix of the maxilla emerges by a foramen close to theexit of the median maxillary nerve (MMN). This lower nerve I refer to as
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FOETAL SKULL OF MESOPLODON STE]NEGERI115

the inferior maxillary nerve (IMN). The last two mentioned nerves probably
correspond to the spheno-palatine nerves.
The presence of the basirostral groove in the foetal skull and its absencein the adult skull, already referred to above, calls for some explanation. As
already observed, the dentary branch enters the so-called basirostral groove
below the maxillary tubercle (MT). Apparently, at an early period of development, the dentary nerve (DN) is intact from the point of emergence from theganglion to the extremity of the rostrum. As growth proceeds secondary bonedevelops at its proximal end and gradually strangles the nerve and blood
supply, eventually cutting off both the neural and vascular supply completely.
This severance of the nerve in lkI. stejnegeri appears to commence some time
before birth, the groove itself gradually filling up, subsequently, with secondarybone, leaving little or no trace of the basirostral groove; however, its erstwhile position is sometimes demarcated by narrow, fragile planges on either
side-its position is often visible throughout the length of the rostrum. Hence,
M. stejnegeri is described as having "no basirostral groove". In the adult ofM. grayi, although the channel is closed off proximally under the maxillary
tubercle (MT), leaving the socalled 'pit', the rest of the channel remains open
permanently.
It is remarkable that, in M. grayi, in which the basirostral groove isalways present, rudimentary teeth frequently occur in the upper jaw, but such
teeth are not socketed in the maxilla, whereas in species devoid of the basirostral groove in the adult, rudimentary teeth have not been observed. Thisobservation seems to suggest that, in M. grayi, the dentary nerve is strangled
at a later period of development than in those species in which the dentarychannel (basirostral groove) is obliterated by the growth of secondary bone.
This suppression of the dentary nerve and blood supply at an early period
of development possibly accounts, at least in part, for the absence of teeth inupper jaws of most Mesoplodon and in other ziphioid whales. However, it isinteresting to observe that, in addition to the functional teeth (in males),vestigial teeth do sometimes occur in some members of the Ziphiidae andtheir presence may be dependent on the extent to which the dentary nerve
has been 'strangled'.
The course of the mandibular branch of the 5th nerve is obviously nottraceable in the foetal specimen. The inferior dental groove is however, open
along its entire length and the functional mandibular teeth are present in thein the rami (one in each). As far as I am aware, rudimentary mandibular
teeth have rarely been observed in Mesoplodon. Fraser (1953) illustrated thepresence of such vestigial teeth in M. bidens. Rudimentary mandibular teeth
have been more frequently reported in Hyperoodon (Boschma, 1950) and in
Ziphius. In Tasmaeetus, the rarest of the family, teeth are present in both
upper and lower jaws. The presence of teeth in both jaws of Tasmaeetus
suggests, perhaps, that it is less specialised than the other ziphioids and retains
part of its more 'primitive' characters.
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McCANNACKNOWLEDGMENTS

My thanks are due to Dr. Sir Robert A. Falla, late Director, National Museum,
Wellington, for the opportunity of undertaking the study; to Messrs F. O'Learyand P. M. Hedgland for the photographs accompany this paper, and, last but
not least, to Miss M. Hall, our Librarian, for her help with the relevant
literature.
REFERENCESBOSCH!v!A, H., 1950. Maxillary teeth in specimens of Hyperodon rostratus (Miller) and Nfesoplodon
grayi von Haast stranded on the Dutch Coast. Proc. K. ned. Akad. Wet. Amsterdam, 53: 775786.
FLOWER, H. H., 1872. On recent ziphioid whales, with a description of the skeleton of Berardius
arnouxi. Trans. Zool. Soc. Land., 8: 203-234.
FORBES, H. 0., 1893. Observations on the development of the rostrum in the cetacean genus
1Vfesoplodon, with remarks on some of the species. Proc. Zool. Soc. Land., 1893: 216-236.
FRASER, F. C., 1953. Report on the cetacea stranded on the British Coasts from 1938-1947. Rep.
Get. (Brit. Mus. Nat. Hist.) No. 13: 1-48.
NoR~IAN, J.R. and F.C. FRASER, 1937. Giant Fishes, Whales and Dolphins. London. pp. 1-361.
OLIVER, W.R. B., 1922. The Whales and Dolphins of New Zealand. N. Zeal. Journ. Sci. &Tech., 5(3): 129-141.
RANKIN, J.J., 1956. The structure of the skull of the Beaked Whale, Mesoplodon gervaisi (Deslongchamps). journ. Morph., 99(2): 229-258.

EXPLANATION OF PLATESPLATE I
Stejneger's Beaked Whale: Mesoplodon stejnegeri True.
adult female showing arrangement of elements.
Courtey Nat. Mus. Wellington, N. Z.
(For explanation of lettering see end of paper)

Lateral aspect of cranium of
Photo P. M. Hedgland

PLATE II
Stejneger's Beaked Whale: Mesoplodon stejnegeri True.
adult female showing arrangement of elements.
Courtesy Nat. Mus. Wellington, N. Z.
(For explanation of lettering see end of paper)

Dorsal aspect of cranium of
Photo P. M. Hedgland

PLATE III
Stejneger's Beaked Whale: JV!esoplodon stejnegeri True. Disarticulated elements of the
foetal cranium.
I. Vomer-presphenoid mass (dorsal aspect); 2. Basisphenoid (dorsal aspect); 3.
Basioccipital (dorsal aspect); 4. Vomer-presphenoid mass (lateral aspect); 5. Maxilla(internal face); 6. Maxilla and palatine bone (external face); 7. Pterygoid bone(external face); 8. Pterygoid bone (internal face); 9a. Interparietal (anterior face);
9b. Interparielal (lateral face); 9c. Interparietal (ventral face); 10. Interparietal
with adjacent frontals (dorsal aspect); Ila. Lachrymal bone (ventral aspect); Jib.
Lachrymal bone (dorsal aspect); 12. Basisphenoid (ventral aspect).
de!. C. McCannSci. Rep. Whales Res. Inst.,
No. 28, 1976.

FOETAL SKULL OF MESOPLODON STE]NEGERIPLATE IV
Stejneger's Beaked Whale: l1{esoplodon stejnegeri True. Disarticulated elements of
foetal cranium.
1. Vomer-presphenoid mass; 2. Basisphenoid; 3. Basioccipital; 4. Supraoccipital;
5. Exoccipitals; 6. Bulla; 7. Periotic bone; 8. Portion of squamosal; 9. Posterior
portion of frontal (damaged); 10. Nasal bone; 11. Orbital portion of frontal(damaged); 12. Lachrymal bone; 13. Premaxilla; 14. Maxilla (posterior portion
incomplete) ; 15. Palatine bone; 16. Pterygoid bone; 17. Mandible (with tooth).
(Excepting nos. 5, 9, paired bones show opposite faces; all other bones show thedorsal aspect on! y.
Courtesy Nat. Mus. Wellington, N. Z.
Photo F. O'Leary
PLATE V
Stejneger's Beaked Whale: /Vlesoplodon stejnegeri True. Showing courses of the main
nerves and vascular supply traced in the rostrum of a foetal specimen (Semidiagramatic).
I. Outer aspect of left rostral portion of maxilla. 2. Transverse section on maxilla.
3. Proximal portion of right maxilla showing maxillary foramen and passage ofpremaxillary branch to premaxillary foramen. 4. Divisions of the 5th cranial
nerve ( Diagramatic).
(For explanation of lettering see end of paper.)de!. C. McCann

EXPLANATION OF LETTERING ON PLATESAN-Antorbital notch.
A T-Antorbital tubercle.
B-Bulla.
BG-Basirostral groove.
BO-Basioccipital.
BOC-Basioccipital crest.
BS.-Basisphenoid.
C-Occipital condyle.
DN-Dentary nerve.
EO-Exoccipital.
F-Frontal.
FO-Foramen ovale.
FP-Falsiform process.
GG-Gasserian genglion.
H-Hamulus.
!MN-Inferior maxillary nerve.
IP-lnterparietal.
K-Keel of vomer.
L-Lachrymal.
MC-Meckel's cavity.
ME-Mesethmoid.
MMN-Median maxillary nerve.
MN-Maxillary notch.

Sci. Rep. Whales Res. Inst.,
No. 28, 1976.

MT-Maxillary tubercle.
MX-Maxilla.
MXC-Maxillary crest.
MXF (MF)-Maxillary foramen.
N-Nasal bone.
NF-'Nasal' nerve foramen.
NR-Anterior nares.
QC-Ossified mesethmoid cartilage.
OG-Optic groove.
OT -Antorbital tubercle.
PL-Palatine bone.
PMF-Post maxillary foramen.
PML-Pterygoid median lamina.
PMX-Premaxilla.
PMXF-Premaxillary foramen.
PS-Presphenoid.
PY-Pterygoid bone.
SO-Supraoccipital.
SQ-Squamosal.
TF-Temporal fossa.
V-Vomer.
VN-Fifth cranial nerve.

117

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McCANN

Sci. Rep. Whales Res. Inst.,
No. 28, 1976.