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The Internal Anatomy
of the Thylacine - A Historical Perspective
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 is the case in placental
mammals. The right and left uteri are also not fused. 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 (1953) published an account of the urogenital system
of the Dasyurinae and Thylacininae in the Papers & Proceedings of the
Royal Society of Tasmania, in which they examined a series of transverse
stained sections of the urogenital system from two female thylacine pup
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. In the
thylacine, the uteri have separate openings into a combined vaginal cul-de-sac.
The lateral and medial vaginae join at the beginning of the urogenital
sinus, into which the urethra from the bladder also empties. Birth
occurs through a central, pseudo-vaginal canal. This short-cut to
the outside forms from the cul-de-sac, where each lateral vagina loops
around a ureter at the base of the uteri. In most marsupials, the
pseudo-vaginal canal opens and closes with each birth. The culs-de-sac
of the thylacine are noteworthy in that they form a fifth of the anterior-posterior
length of the vaginal complex. Pearson & de Bavay (1953) state:
"It is important
to note that even in these extremely immature specimens the culs-de-sac
have reached a higher stage of development than that found in mature specimens
of Antechinus". |
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| A
comparison of the monotreme, marsupial and placental reproductive/excretory
systems. |
In marsupials, the outlets
of the female reproductive and excretory systems are somewhat less widely
spaced than in many placental mammals, and are contained within a single
external vent. However, it is not like the true cloaca of the monotremes
(e.g. echidna and platypus), in that the urethral and rectal outlets are
separate. In monotreme mammals, the passages of the uterus, bladder
and rectum all open into a cloaca, one of a number of reptilian characteristics
that they have retained. The term monotreme means "one
opening" in Greek.
R. Leon Hughes
(2000), in a paper entitled "Structure of the female reproductive tract
of an adult parous Tasmanian tiger, Thylacinus cynocephalus" published
in the Australian Journal of Zoology, completed the pioneering work
initiated by Pearson & de Bavay in describing the reproductive tract
of Hill's adult female specimen, then located in the Hubrecht laboratory
in the Netherlands. Hughes notes:
"As in other marsupials,
the reproductive tract was characterised by the presence of a uterus duplex
and a vaginal complex where the ureters passed dorsally over each lateral
vaginal canal to enter the bladder. The lateral vaginal canals each
entered a urogenital sinus that terminated in a shallow cloaca. The
gross dimensions of the reproductive tract of the thylacine were greater
than those of any extant dasyurid marsupial. The distance from the
rostral pole of the ovaries to the most caudal extremity of the urogenital
sinus measured 25 cm. The distinctive aspects of the reproductive
tract included a disproportionate enlargement of the corpus uteri that
is without |
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| Reproductive
tract of the female thylacine - drawn from the "wet" specimen in the collection
of the Museum für Naturkunde (Berlin). |
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parallel in any other marsupial species.
The bodies of the right and left uteri measured 10.4 cm 1.2 cm 0.9 cm and
9.1 cm 0.8 cm 0.7 cm respectively. The rostro-caudal length of the
right and left cervices measured 2.7 cm and 1.7 cm respectively.
The cervical canals entered the vaginal complex by way of a thick median
vaginal septum. The elongated caudal component of the vaginal culs-de-sac
lacked a median vaginal septum. As in other dasyurid marsupials,
the lateral vaginae and associated vaginal complex were of diminutive proportions
in relation to the typical marsupial pattern". |
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