EPIDERMAL CYST IN THE NECK OF
A KILLER WHALE
TOSHIRO KAMIYA
Department ef Anatomy, Faculty ef Medicine, University of Tokyo, TokyoTERVO TOBAYAMAKamogawa Sea World, Chiba

AND
MASAHAR U NISHIW AKI
University ef the Ryukyus, Naha, Okinawa
Two killer whales with small recess in the skin on the anterior rim of the forelimbwere reported by Nishiwaki (1973)*. One killer whale in Vancouver Public
Aquarium showed a pair of recesses on the right and the left on the anterior rimof the forelimb and another one in Kamogawa Sea World, Chiba showed a single
recess on the right side of the cranio-ventral rim of the forelimb (Fig. 1).
Nishiwaki regarded these recesses as vestigial teats in view of their sites, atthe same time pointing out a high possibility of the occurrence of similar structure
in other cetacea especially killer whales. Among these two killer whales withrecess reported by Nishiwaki, the killer whale in Kamogawa Sea World died ofliver dysfunction in July 1975 (body length 533 cm, body weight 1,600 kg, male).
Autopsy performed to clarify the cause of death revealed the nature of the recess
in question as a tube shaped epithelial pocket with the diameter of 5 mm anddepth of 8 cm as shown in Fig. 2.
The recess enters vertically from the superficial layer into the corium and theoutside of the tip is surrounded by thick and firm capsule-like structure consistingof connective tissue. The shape of the tip of the aberrant epithelium appears likean ending with alveolar and ductal branching as if blocked by the thick capsulelike external wall. The lumen of the tubular recess is filled by abrased epithelium
appearing as cerumen. From the origin of the recess to the end of the surrounding
tissue, no glandular structure was found at all macroscopically and histologically,and no nerve endings were found. Within the connective tissue surrounding theterminal portion of the recess, however, melanocyte-like cells were found scattered.
Based on the present autopsy findings, the recess in the skin of the killer whales
reported by Nishiwaki was found to correspond to the pathological picture of epidermal cyst in man. Unlike the epidermal cyst in man the recess in killer whale
is characterized by the presence of melanocyte-like cells in the connective tissue
surrounding the tip of the recess. No epidermal melanocytes are found in the* Nishiwaki, M., 1973.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979, 93-94

Possible vestigial teats of killer whales.

Sci. Rep. Whales Res. Inst., 25: 277-278.

94

KAl
¥ll
YA,TOBAYAMAA:'¥DNISHl¥¥'AKI

も「司よと4一−:rL 注E,,.
̲『哩－』幅~』l、Fig.l. Thebell
yoft
hekillerwhaleo
fa5
33cmlength.malei
nKamoga
waSeaVorl
d.A
rr
ows
howt
hes
ma
lr
ecessont
hec
r
an
io
‑v
entr
a
lri
mri
ghtoft
h
efore
li
mb.

F
i
g.2.L
on
gi
tu
di
n
alsec
t
io
nt
hrou
g
hs
ma
l
lr
e
ces
so
fk
i
l
le
rw
haleo
fa5
33cml
en
g
t
h,
ma
le. :
'¥ot
icethelume
nofr
ecessandt
hickand白rmc
ap
su
le‑
li
kestr
u
ctur
eofconnc
cuv
ci
tssue.
normalcoriumoft
hecetacea. Nootherr
e
por
t
sar
eav
ai
labl
eonepidermalc
ysti
nt
hec
etac
ca, and thecause r
ema
insunknown. Aswas pointed outbyNishi‑
waki,however,demonstration ofsuch cysti
n two killer whales being localizedi
nt
hene
ckwoulds
uggesttheneedforfutu
reobser
v
ati
ont
oc
lecic
lewh巴thcrornot
suchc
ysto
ccur
sf
requ
e
nt
lyi
nki
lle
rwhal
es.
S
ci.Re
p.W
/i
(l/esRe
s.I
nst.
,
λfo.3
1.1979