.
BIOLOGY:
- ANATOMY -
INTERNAL ANATOMY (page 7)
.

 
.
The Internal Anatomy of the Thylacine - A Historical Perspective

    Bernard William Tucker (1901-1950), was demonstrator in Zoology and Comparative Anatomy at Oxford University.  He performed a detailed dissection and study of the head of the London Zoo's last female thylacine, that was on display at the zoo from 26 January 1926 until her death on 9 August 1931.

.
London Zoo's last thylacine (1926)
.
London Zoo's last thylacine, 1926.  Courtesy: Zoological Society of London.
.
    Surprisingly, in his report of 1882, Cunningham did not make any comment on the anatomy of the head of either of his specimens.  Tucker was somewhat astonished when asked to undertake the study that virtually nothing had previously been written on the subject.  Tucker states: 

    "Considerable attention has been paid to the head and neck musculature of marsupials and naturally a certain amount of information on the cranial nerves and blood vessels is scattered throughout the literature, but nowhere could I find the kind of coherent and comprehensive account of these portions of the anatomy of a marsupial type which I had expected would afford a basis of comparison with Thylacinus.  No doubt a partial explanation of this astonishing state of affairs is that morphologists have found the cranial anatomy of the marsupials so closely similar to that of the placentals.  This similarity, indeed, is well known.  Yet it seems very strange and highly unsatisfactory that there should be any part of the anatomy of a whole sub-class of mammals of which a full and connected account is not available.  This consideration, together with the fact that the extreme rarity of Thylacinus seemed to render it almost a duty to make the fullest possible use of the material, convinced me of the need to make a more detailed study than I had first visualised".

    Tucker examined both the arterial and venous flow, and the deep and superficial nerve supply to the head, and produced comprehensive notes and working drawings of his findings.  His study of the cranial anatomy is still the most detailed ever produced.  He also wrote a full account of the musculature of the neck and shoulder.  Tucker's unpublished notes and drawings are now held in the collection of the Oxford University Museum, together with the remains of the dissected head (Specimen OUM 7942) (Source: ITSD 4th Revision 2011).

.
dissection of the neck musculature of the thylacine - S. Sleightholme (after Tucker)
.
Dissection of the neck musculature of the thylacine.  Drawing: Dr. Stephen Sleightholme (after Tucker).
.
    Professor Dr. Heinz Friedrich Moeller (1936-2009), was the Director of the Zoological Museum and the Department of Comparative Morphology of Vertebrates at the University of Heidelberg.  He was internationally regarded as a leading authority on the zoology of the thylacine, publishing a series of papers and a book, "Der Beutelwolf", on the subject (view details on "Der Beutelwolf").

    In 1968, Moeller published a paper, "Zur Frage der Parallelerscheinungen bei Metatheria und Eutheria. Vergleichende Untersuchunge an Beutelwolf und Wolf", in which he noted that the brain of the thylacine is considerably smaller in relation to body size than that of the placental wolf.  The average capacity of the braincase was 53.5 cc as measured by Moeller on a series of 30 thylacine skulls.  In an equal number of wolf skulls, the braincase capacity was 134.4 cc.  The average length of the thylacine skulls was 207.1 mm, compared to an average length of 213.4 for the wolf skulls.

.
comparative marsupial brain studies
.
Comparative brain studies of the quoll (Dasyurus), Tasmanian devil (Sarcophilus) and thylacine (Thylacinus) in lateral, dorsal and ventral view.

    In 1970, Moeller published the most detailed account to date on the comparative studies of the brain of the greater dasyurids (Thylacinus, Sarcophilus and Dasyurus) with respect to their evolutionary status in a paper entitled: "Vergleichende untersuchungen zum evolutionsgrad der gehirne groBer Raubbeutler (Thylacinus, Sarcophilus und Dasyurus. I. Hirngewicht. II. Hirnform und Furchenbild".

Click the microscope icon for a magnified view of: lissencephalic brain.
Click the microscope icon for a magnified view of: gyrencephalic brain.
    Moeller notes that the brain of Dasyurus is lissencephalic from the Greek "Lissos" = smooth, hence, a smooth-surfaced or non convoluted brain.  The brain of Sarcophilus shows only a few furrow-like impressions.  The brain of Thylacinus is gyrencephalic from the Greek "Gyros" = ring (gyrus), and "Enkaphale" = brain.  Gyrencephalics have folded or convoluted brains.

    Moeller observed that when comparing the outward appearance of the brains, and the casts of the braincases, that the neocortex of Sarcophilus, and to a higher degree that of Thylacinus, is enlarged.  This enlargement in Thylacinus goes hand in hand with diminishing of the olfactory parts of the brain.  The surface expansion of cerebral cortex is one of the most distinguishing evolutionary features of the mammalian brain. The cerebral cortex is responsible for higher cognitive functions and is thought to underlie the concomitant growth in intellectual capacity.

    Note:  The marsupial brain is smaller than that of a placental mammal of similar size and lacks a corpus callosum, a structure that permits nerve communication between the right and left cerebral hemispheres.  Marsupials however, have an enlarged anterior commissure that serves a similar purpose.

thylacine endocranial cast
.
Lateral views of the thylacine brain (endocranial cast) from the right, front, left and back.  A 360° rotational view of this cast can be seen here.
.
.
References
.
back to: Internal Anatomy (page 6) return to the subsection's introduction forward to: Internal Anatomy (page 8)


Search the Thylacine Museum
Site Map
Website copyright © C. Campbell's NATURAL WORLDS.
Photographs and other illustrations (where indicated) are © C. Campbell's NATURAL WORLDS.
Other photos and images are © their respective owners.