MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 355 



periods of gestation, and the powers of the new-born foetus. As far, however, as a 

 conclusion can be drawn from the relative periods of gestation in the Kangaroo and 

 Opossum, the proportionate capacities of the vaginae to the uteri would appear to be 

 inversely as that period ; and that while the vaginae are calculated to present fewer 

 obstacles to the escape of the foetus in proportion to the duration of its uterine ex- 

 istence, so a less capacious and complete external pouch is requisite for its ultimate 

 perfection. From Rengger's description of the connexion of the foetal Opossum to 

 the uterus, it might be concluded that the generation in that animal approximated to 

 the true viviparous mode more nearly than in the Kangaroo ; but the determination 

 of this interesting question will require a more exact investigation into the nature of 

 the foetal vessels and membranes in the genus Didelphys. The impregnated uteri of 

 the smaller pouchless Opossums of South America would be objects of peculiar in- 

 terest and value in the present state of the inquiry. 



With respect to the variations of structure in the marsupial female organs, it may 

 also be remarked, that though they are apparently most complicated in the Kangaroos 

 and Phalangers, yet in reality they deviate from the type of the normal Mammalia 

 in a minor degree in these Marsupiata than in the Didelphides and Petaiiri. For the 

 essential diflference being a division of the vagina into two canals, we find this to be 

 most complete in the latter genera, while in the Kangaroos the division is only 

 partial, and the complexity arises more from augmented capacity and extent. 



Now it is important to observe, that the fission of the efferent tube is not continued, 

 as might naturally be supposed, from the uterus into the vagina, leaving its distal 

 extremity single, but commences at the urethro-sexual cavity, and is arrested near 

 the uteri, the orifices of which thus open into a common canal. 



The situation of the rudimentary vaginal septum or hymen in the unimpregnated 

 female organs of the normal Mammalia before mentioned corresponds with this for- 

 mation in the Kangaroo ; and in a case where this septum was preternatu rally de- 

 veloped in the human subject, it was found to obey the same law of formation, and 

 at the same time to have been coincident with a completely divided uterus. 



This malformation, so remarkably analogous to the structure of the marsupial 

 uterus, is described by Dr. Purcell in the sixty-fourth volume of the Philosophical 

 Transactions, and the specimen itself is in the Museum of the Royal College of Sur- 

 geons*. The vaginal septum is vertical, commencing at the outlet, and terminating 

 about an inch from the orifices of the uteri ; and, as Dr. Purcell accurately describes, 

 it is " not merely membranous, but fleshy, and of a considerable thickness ; and like 



* I have subsequently witnessed, through the kindness of my friend Dr. Thomas Blundell, an accurate 

 model of a similar malformation of the vagina in the human subject : the vertical septum commenced at the 

 vaginal outlet, and extended backwards for an inch, dividing the passage for that extent into two lateral 

 canals. The indiiidual underwent an operation for its removal. In this case the condition of the uterus could 

 not of course be ascertained ; but my friend Dr. Lauth of Strasburg has described and figured two preparations 

 in the Museum of the Faculty of Medicine in that city analogous to the case described by Dr. Purcell. In 

 one of these the uterus was divided internally into two lateral chambers, and the whole of the vagina was 



