148 
Total length, 18 inches; bill, 44; wing, 6; tail, 74; tarsi, 13. 
Hab. Santa Fé de Bogota. 
In the collection of Prince Massena at Paris. 
Professor Owen read a communication on the Rudimental Mar- 
supial Bones in the Thylacinus :— 
The marsupial bones, as bones, do not exist in the Dog-headed 
Opossum or Hyzena of the Tasmanian colonists (Thylacinus Harrisii, 
Temm.); they are represented by two small, oblong, flattened fibro- 
cartilages, imbedded in the internal pillars of the abdominal rings, 
and appear each as a thickened part of the tendon of the external 
oblique abdominal muscle, which forms the above pillar. The length 
of the marsupial fibro-cartilage is six lines, its breadth from three 
to four lines, its thickness one line and a half. 
This was the condition of the rudimental marsupial bones in two 
full-grown females and one male specimen of the Thylacinus: ina 
fourth large and old male a few particles of the bone-salts were de- 
posited in the centre of the fibro-cartilage, occasioning a gritty feel- 
ing when cut across by the knife. 
This unexpected and very remarkable modification of the most 
characteristic part of the skeleton of the Marsupialia, in one of the 
largest of that order, has many important bearings upon the physio- 
logy of the problematical ‘ ossa marsupialia.” They have been most 
commonly supposed to serve for the support of the marsupial pouch 
and young ; but this pouch is well developed in the female Thylacine, 
and in one of the specimens which I dissected four well-developed 
teats, each two inches long, indicated that it had contained four 
young ones when, or shortly before, it was killed. The existence 
of the marsupial bones in the male as well as the female sex in other 
marsupial animals had already invalidated the above physiological 
explanation, and it equally opposes the idea of the use of the mar- 
supial bones, propounded by M. de Blainville,—that they aid in the 
compression required to expel the embryo. Besides, it is not in the 
females of those animals which give birth to the smallest young that 
we should expect to find auxiliary bones for increasing the power of 
the muscles concerned in parturition. My view of the uses of the 
marsupial bones, as explained in the ‘ Philosophical Transactions’ for 
1834, is, that they relate more immediately to an increase of power 
in the muscles (cremasteres) which wind round them, than of those 
implanted in them: and to the extent to which the cartilaginous 
representatives of the ossa marsupialia in the Thylacine strengthen 
the pillars of the abdominal ring, they must increase the contractile 
force of the compressors of the mammary glands and teats, which 
are situated and surrounded by the cremasteres in the Thylacine, as 
in other Marsupialia. Nevertheless, the almost obsolete condition of 
the ossa marsupialia in the Thylacine, and their very various relative 
sizes in other Marsupialia, are circumstances which seem incompa- 
tible with the same kind and degree of use in all the species: they 
are very slender, and not above half an inch in length m the Myr- 
mecobius, whilst in the Koala they nearly equal the iliac bones in size. 
