The Internal Anatomy of the Thylacine
- A Historical Perspective
(continued)
.
In recent years, the work
of Professor Heinz F. Moeller has greatly expanded our understanding
of comparative anatomy with respect to the thylacine. Moeller (1968)
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.
Moeller (1970) also
published the most detailed account to date on the comparative studies
of the brain of the greater dasyurids (Thylacinus, Sarcophilus
and Dasyurus) with regard to their evolutionary status. He
notes that the brain of Dasyurus belongs to the lissencephalic
type and that of Sarcophilus shows only a few furrow-like impressions;
the brain of Thylacinus belongs to the gyrencephalic
type. Moeller notes that when comparing the outward appearance of
the brains and the casts of the braincases that the neocortical portion
of Sarcophilus and to a higher degree that of Thylacinus
is enlarged. The lateral enlargement as well as the lower portion
of the sulcus rhinalis and the neocortical overlapping of the tectum mesencephali
give evidence of a growing neocorticalisation of Thylacinus going
hand in hand with diminishing of the olfactory parts of the brain.
.
| Comparative
brain studies of the quoll (Dasyurus), Tasmanian devil (Sarcophilus)
and thylacine (Thylacinus) in lateral, dorsal and ventral view. |
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 have an enlarged
anterior commissure that serves a similar purpose.
.
| Reproductive
tract of the female thylacine - drawn from the "wet" specimen in the collection
of the Museum für Naturkunde (Berlin). |
|
The reproductive tract of the female thylacine, which
is much like that of dasyurids, was first described by Pearson &
de Bavay (1953), and again by Moeller (1997)
and more recently by R. Leon Hughes (2000). Marsupial and
placental mammals differ markedly in their reproductive anatomy.
In female marsupials the reproductive tract is duplicated. The right
and left vaginae are separate structures and are not fused as would be
the case in placental mammals. The right and left uteri are also
unfused. The ovary is enveloped by the delicate membranous fimbria
(finger-like process), which are an extension of the infundibulum of the
oviduct (funnel-shaped opening of the fallopian tube adjacent to the ovary)
into which the eggs are shed. The eggs pass into the ampulla, which
is an expanded region of the oviduct (Fallopian tube) and this is where
fertilisation occurs. The ampulla leads into the isthmus, a convoluted
section of the oviduct, which in turn leads into the uterus. |
Joseph Pearson and J.
M. De Bavay published an account of the urogenital system of the Dasyurinae
and Thylacininae in the Papers & Proceedings of the Royal Society of
Tasmania Vol. 87 (1953) in which they examined a series of transverse stained
sections of the urogenital system from two female thylacine cub specimens
in the Australian Museum and Museum Victoria collections.
They noted that as their
interpretation was based on immature material it lost much of its value
with respect to determining the precise arrangement of the urogenital system
in a mature female of the species. |
