1865. Philosophical Transactions for 1834. 311 



The anatomical descriptions are illustrated by drawings, which will 

 be found particularly serviceable in unravelling, as far as anatomy 

 can at present carry us, some of the intricacies of the cerebral organ. 

 The pons varolii, we observe, in an especial manner, has received 

 much attention from the distinguished author. 



The generation of Marsupial animals, which constitute a distinct 

 tribe of mammalia, of which the kangaroo and opossum are the prin- 

 cipal members, has hitherto been involved in much obscurity. But 

 Mr. Owen, who has been fortunate enough to have it in his power 

 to examine the gravid uterus of a kangaroo, has observed some im- 

 portant facts. The genera of this tribe are characterized by possessing 

 a double uterus, and the true vagina is separated either wholly, or 

 for a considerable extent, into lateral canals, while the digestive and 

 generative tubes both terminate within a common cloacal outlet. In 

 these respects, therefore, they approach the oviparous vertebrata. 

 The foetus examined by the author was contained in the left uterus. 

 No placental structure could be observed. The chorion was very 

 thin. A transparent amnios enveloped this foetus. The umbilical chord 

 was two inches in length ; the uterus two inches in length, and above 

 an inch in diameter. No perceptible trace of an allantois or urinary 

 bladder could be detected ; but in another foetus two weeks old, a 

 urachus was detected. The author concludes from the observations 

 of others, coupled with his own, that the ovulum quits the ovisac 

 as in ordinary mammalia. In the kangaroo uterine, gestation 

 continues 39 days ; in the opossum 26 days. The former has been 

 determined with certainty in the Zoological Gardens, and therefore, 

 overturns the statement of Hilaire, who made the period 4 months. 



With regard to the relation between the size of the umbilical 

 vesicle, the least vascular placenta and a corresponding simplicity of 

 brain, it appears that in the kangaroo, although shortly after birth the 

 brain resembles in structure that of the lowest vertebrata, yet it 

 afterwards assumes a more complex form than that of the opossums 

 or dasyures. The individuals of the marsupial tribe seem low in in- 

 telligence, never manifesting any sign of recognition of their keepers 

 or feeders, and being unable to utter vocalized sounds. When they 

 are irritated they emit a wheezing or snarling guttural sound, the 

 necessary apparatus for producing vocalized sounds being absent. 

 In this respect they resemble the reptilia. 



In the author's communication on the ornithorhyncus para- 

 doxus, this idea of similarity and that lactation might co-exist with 

 a mode of generation essentially similar' to that of the viper and sa- 

 lamander is fully confirmed. The regular gradation is traced which 

 exists in different orders of mammalia, in which true viviparous or 

 placental generation takes place, towards the ovo-viviparous or ovi- 

 parous modes, in which the exterior covering of the ovum never be- 

 comes vascular. The ornithorhyncus is shewn to constitute a con- 

 necting link in the chain. Both of these papers are accompanied by 

 plates. 



Mr. Lister has observed the existence of currents within some 



