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The Internal Anatomy
of the Thylacine - A Historical Perspective
Frank Evers Beddard
(1858-1925), was prosector to the Zoological Society in London (1884-1915),
and a lecturer in Biology at Guys Hospital Medical School. In 1884,
the Zoological Society in London purchased a male and female thylacine
from Dr. Bingham Crowther of Launceston. Both of the thylacines were
classed as near-adults. They arrived at the London Zoo on the 14th
November 1884. The male died on the 5th February 1890; the female
on the 2nd April 1893. Beddard dissected the male thylacine and went
on to describe both the scrotal pouch and brain in the Proceedings of
the Zoological Society (Beddard 1891). He was surprised to find
a rudimentary "pouch" present in the male, but recalled that Sir
Richard Owen had observed this feature many years previously (Todd 1874): |
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| "In
the male Thylacine the rudimental marsupium is retained, in the form of
a broad triangular depression or shallow inverted fold of the abdominal
integument, from the middle of which the peduncle of the scrotum is continued.
In the female the orifice of the capacious pouch is situated nearer the
posterior than the anterior boundary of that receptacle" - R. Owen.
Beddard states:
"As the organ in
the male Thylacine has not to my knowledge been illustrated, I have thought
it desirable to have the accompanying drawing prepared. The figure
shows the pouch, which was sketched by Mr
Smit immediately after the death of the animal, and the scrotum
containing the testicles, which descends from the interior of the pouch.
The drawing also shows that there is not merely a tract of naked skin surrounding
the testes, but a deepish pouch which is overhung by the surrounding integument;
the pouch is deepest in front and gradually gets shallower behind; it follows
therefore that the pouch is directed backwards as in Perameles. The
general outline of the pouch is oval, or rather pear shaped, for there
is a narrow continuation of it backwards; the scrotum supported on a short
stalk descends from the interior of the pouch nearer to the posterior than
the anterior extremity". |
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Smit's illustration
of the "pouch" of the male thylacine. Source: Proceedings
of the Zoological Society of London, (1891), Fig. 1, p. 139.
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| One glaring omission
is absent from Smit's illustration, and that is the position of the thylacine's
penis.
Paddle
(2000), in his book "The Last Tasmanian Tiger", notes:
"What Smit had available
to him, as objective evidence, and what he actually illustrated appear
as two different realities. Bound by a dominant placental discourse,
Smit worked on the assumption that all male mammals are built in the same
way, the way in which he was most familiar, with the penis positioned anteriorly
(closer to the head) than the scrotum. While possibly for reasons of propriety
the thylacine's bifid penis was not included in the illustration, it obviously
belongs at the bottom of the picture. Smit, attempting a little permitted
verisimilitude, indicated the positioning of the tail at the top of the
plate. Unfortunately, not all male mammals are built the same way.
In marsupials it is the scrotum which lies anteriorly, with the penis positioned
closer to the tail. The essential error propounded by Smit was his
placement of the tail at the wrong end of the illustration". |
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| A
sleeping male thylacine at the Beaumaris Zoo (SB), circa 1916. The
tail of another individual can be seen extending from the right.
Although
the scrotum of the thylacine is often held within a kind of "pseudo-pouch"
formed by surrounding folds of skin, the above photo illustrates that this
is not always the case (at least, not at times when the animal is in a
relaxed state). Rather, the scrotum normally hangs
suspended below the level of said skin flap, as is so with the
closely related Tasmanian devil. While some non-technical references
have mentioned that in the thylacine both sexes possess pouches, it is
important to point out that the insunk, pocket-like area which surrounds
the male's scrotum is in no way similar to the true marsupium
of the female, which is of course used to carry the young. |
Beddard continues his
paper with a description of the thylacine's brain. He notes that
the total length of the brain as measured from the end of the cerebellum
to the anterior extremity of the olfactory lobe as being 76 mm (3 in.)
and that the greatest length of the cerebral hemispheres was 48 mm (1.89
in.) with a height of 26 mm (1.02 in.). Beddard then discusses the
historical observations that were made on the thylacine brain by Flower
(1865) and Owen (1868), and from an endocranial cast by Gervais (1837)
and states:
"Since the thylacine
is an animal which is getting scarcer, I have thought that an attempt at
a fuller description of the brain than is to be found in the memoirs cited
might be acceptable". |
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Diagram
of the left side of the thylacine brain. Source: Dr Stephen
Sleightholme. ITSD 5th Revision 2013.
Dr. Sleightholme notes that
preservation of a brain in alcohol will inevitably cause tissue shrinkage
over time, and the measurement given in the above photograph would not
necessarily reflect that of a freshly dissected brain, or for that matter,
a living example. |
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| Beddard proceeds to
compare the structure of the thylacine brain with that of the Bennett's
wallaby (Halmaturus bennetti =Macropus rufogriseus) and
koala
(Phascolarctos cinereus) with specific reference to the position
of the cerebellum and cerebral hemispheres.
He notes that the cerebral
hemispheres in the thylacine are not greatly convoluted, but when compared
to the opossum (Didephis sp.), and the Tasmanian devil (Sarcophilus
harrisii), the degree of convolution increases between the smaller
and larger forms. He further notes that the sulci are less numerous
and shallower in the thylacine brain when compared to that of a kangaroo
of similar size. Beddard concludes with a discussion on the lobar
divisions and specific arrangement of the fissures of the cerebral hemispheres
with reference to other species including the extinct Marsupial lion -
Thylacoleo
(shown below). The preserved brain of Beddard's specimen is now in
the collection of the Oxford University Museum (Source: ITSD 5th Revision
2013). |
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In the Proceedings
of the Zoological Society of London, Beddard (1903) is noted as displaying
sections of the ovary of the thylacine:
"Mr F. E. Beddard also exhibited
and made remarks upon sections of the ovary of Thylacinus which showed
the immigration of the follicular cells into the ova". |
