316 



MARSUPIALIA. 



others partially divided ; but the divided por- 

 tion in the latter is always that which is nearest 

 the urethro-sexual passage. 



The true uterus is completely divided in all 

 the Marsupial genera, and each division is of a 

 simple elongated form, as in the Rodentia. 



The superadded complications in the female 

 generative organs of the Marsupials, as com- 

 pared with other mammals, are not then rightly 

 attributable to the uterus, but to the vagina ; 

 and they are of such a nature as to adapt the 

 latter to detain the foetus, after it has been ex- 

 pelled from the uterus, for a longer period than 

 in other Mammalia. 



These complications vary considerably in the 

 different marsupial genera. On a comparison 

 of the female organs in Didelphys dorsigera, 

 Petaurus pygnueus, and Petaurus taguanoides, 

 in Dasyurus viverrinus, in Didelphys Virgi- 

 niana, in Macropus major, and Hypsiprymnus 

 murinus, I find that the relative capacity which 

 the uteri bear to the vaginae diminishes in the 

 order in which the above-named species follow, 

 while the size of the external pouch increases in 

 the same ratio. 



In Didelphys dorsigera the uteri (Jig. 139, 

 c, c,) rather exceed the unfolded vaginae in 



Fig. 139. 



Didelphys dorsigera. 



length. In most Marsupials the vaginae at 

 first descend as if to communicate directly 

 with the urethro-sexual passage ; but in this 

 small Opossum, in which the abdominal pouch 

 consists of two slight longitudinal folds, and 

 the young, as is implied by its trivial name, 

 are transported by the mother on her back, 

 each vaginal tube (e, e, f fig. 139,) after em- 

 bracing the os tincae (d), is immediately con- 

 tinued upwards and outwards, then bends 

 downwards and inwards, and, after a second 



bend upwards, descends by the side of the 

 opposite tube to terminate parallel with the 

 extremity of the urethra (h) in the common 

 or uro-genital passage (j'). 



In the Petauri, the vaginae, when unfolded, 

 are a little longer than the uteri. On examining 

 a specimen of the Pigmy Petaurist which had 

 two very small young in the pouch, I found 

 both the true uteri of three times the diameter 

 of the same in an unimpregnated specimen ; 

 but the vaginae were unaltered in size, indi- 

 cating that the situation in which gestation 

 takes place in this species is the same as in the 

 Kangaroo. The vaginae, after receiving the 

 uteri, descend close together half-way towards 

 the commencement of the urethro-sexual pas- 

 sage, but do not communicate together in this 

 part of their course. From the upper part of 

 these culs-de-sac they are continued upwards 

 and outwards, forming a curve, like the han- 

 dles of a vase, then descend, converge, and 

 terminate close together, as in the preceding 

 example. 



In Dasyurus viverrinus and Didelphys Vir- 

 giniana, the mesial culs-de-sac of the vaginae 

 descend to the urethro-sexual passage, and are 

 connected to, but do not communicate with it. 

 The septum dividing them from each other is 

 complete, being composed of two layers which 

 can be separated from each other, and which 

 result indeed from the apposition and mutual 

 cohesion of the vaginae at this part. In order 

 to reach the common passage, each tube is con- 

 tinued outwards from the upper end of the cul- 

 de-sac, and forming the usual curve, terminates 

 parallel to the orifice of the urethra. The 

 vaginae in the Dasyures are smaller in propor- 

 tion to the uteri than in the Virginian Opossum, 

 but of a similar form. 



In another species, the Didelphys Opossum 

 of Linnaeus, it would appear from the descrip- 

 tion and figures of Daubenton,* that the septum 

 of the mesial culs-de-sac of the vaginae was im- 

 perfect ; but it is doubtful whether this inter- 

 communication was not the result of parturition, 

 or of an accidental rupture in the specimen ex- 

 amined. If it should prove to be a specific 

 difference of structure, it is an approximation 

 to the condition of the female organs in the 

 Phalangers, the Wombat, and the Kangaroos. 



In the Mucropus major the vaginas (jig. 138, 

 e, e') preponderate in size greatly over the uteri 

 (r, c') ; and, the septum (e") of the descending 

 cul-de-sac being always more or less incom- 

 plete, a single cavity (e) is thus formed, into 

 which both uteri open ; but however imperfect 

 the septum may be, it always intervenes and 

 preserves its original relations to the uterine 

 orifices (d, d). 



The foetus has been conjectured to pass into 

 the urethro-sexual cavity by a direct aperture 

 formed after impregnation at the lower blind 

 end of the cul-de-sac, but I have not been able 

 to discover any trace of such a foramen in two 

 kangaroos which had borne young ; and be- 

 sides, I find that this part of the vagina is not 

 continuous by means of its proper tissue 



* Buffon, Hist. Nat. torn. x. p. 279. 



