The Internal Anatomy of the Thylacine - A Historical Perspective

    Professor Daniel John Cunningham (1850-1909), was Senior Demonstrator in Anatomy at the University of Edinburgh (1876-1882) and chronologically thereafter Professor of Anatomy at the Royal College of Surgeons of Ireland (1882-1883), Trinity College Dublin (1883-1903), and Edinburgh University (1903-1909).  Whilst acting as Demonstrator in Edinburgh, Cunningham wrote an extensive report on the anatomy of the Marsupialia collected during the voyage of HMS Challenger, a memoir which established his reputation as an able, descriptive anatomist and capable elucidator of difficult morphological problems (Thomson 1909).  Much of what we know today about the internal anatomy of the thylacine is derived from Cunningham's meticulous anatomical dissections, and published as part of the HMS Challenger report in 1882 (Cunningham 1882).

HMS Challenger farewell to Sydney (1874)
HMS Challenger farewell to Sydney, June 8th 1874.
Artist - John J. Arthur.  Courtesy: State Library of Victoria.
    The HMS Challenger expedition returned to England in 1876 after circumnavigating the world to learn more about the oceans.  Aboard were the remains of a male and female thylacine, preserved in barrels of spirit, presented by the Governor of Tasmania (Sir Charles Du Cane) whilst Challenger was berthed in Sydney (1874).
Challenger thylacine specimen - ITSD
Challenger thylacine specimen
(female) 1883-8-22 (10,11,12).
Courtesy: British Museum Natural History.
Source: ITSD 5th Revision 2013.
    Cunningham notes: 

    "The male had manifestly been received in a very putrid state, but its long immersion in strong spirit had considerably improved its condition.  The female was in an admirable state of preservation, and it is consequently from it that the majority of the drawings have been taken and the description framed. A special interest is attached to the anatomy of this animal, from the very prevalent belief that the genus of which it is the sole member is rapidly becoming extinct.  Thus Owen, writing in 1842 speaks of it as a species "whose term of existence seems fast waning to its close".

    Cunningham opens his report with a detailed comparison of the musculature of the fore and hind limbs of the thylacine (Thylacinus cynocephalus) with that of a specimen of the Spotted cuscus (Phalangista maculata =Spilocuscus maculatus) and of the Red-tailed Phascogale (Phascogale calura), highlighting both their structural similarities and differences.  He details the origin and insertion of the various muscle groups with respect to the three species.

    Due to the reduction of the clavicle in the thylacine, a rerouting of the muscles normally attached to it was noted.  The cleido-mastoid is partially inserted into the inner portion of the clavicle and partly joins the clavicular area of the deltoid muscle.  The scapular section of the deltoid muscle is enlarged, and unlike the dasyurids, there is no spinal section.  The subclavian muscle

cannot be inserted into the upper margin of the clavicle.  Instead, it runs beneath the clavicle, changes direction, and inserts into the fascia which covers the supraspinatus.  The supinator longus is not well developed, and the anconeus externus is absent.  As an adaptation to running however, the triceps is quite large.  Also, the pectoralis minor is rather well developed compared to its usually small size in dasyurids.  The pectoralis quartus is small and quite basic.

    Cunningham begins his summary on the structure of the internal organs with comments on the pericardium and its specific attachments before proceeding to discuss the external appearance and internal structure of the heart.  He notes that the thylacine's heart is narrow, elongated and pointed with a very capacious right auricle and its appendix, whilst showing no indication of bifurcation is peculiar on account of its great breadth.  Cunningham then discusses his observations on the internal structure of the chambers of the heart and concludes by noting two distinguishing features of the marsupial heart; the absence of all traces of an annulus ovalis and fossa ovalis and the peculiar position of the right auricle of the orifices of the great cardiac vein.

Marsupialia Plate IV - Thylacine, from The Voyage of H.M.S. Challenger
Marsupialia Plate IV - Thylacine, from "The Voyage of H.M.S. Challenger" (1882).
Fig. 1 - Internal aspect of the thigh.
Fig. 2 - Dissection to show the gluteus quartus muscle.
Fig. 3 - Marsupial pouch of the female.
Fig. 4 - Dissection of the marsupial pouch - teats left in position.
Fig. 5 - Gluteal region and outer aspect of the thigh.
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