124 



MARSUPIAL " I,ARVAE 



are the precise equivalents of similar bones in the jMonotreniata. 

 It has been held, but apparently erroneously, that these bones 

 are mere ossifications in the tendons of the external oblique 

 muscle of the abdomen, or of the pyramidalis of the same region ; 

 and vestiges have been asserted to exist in the Dog. Such 

 bonelets are undoubtedly present in the 

 Dog ; but it seems clear from their develop- 

 ment in Mai'supials, as structures actual!}- 

 continuous with the median unossified x)or- 

 tion of the symphysis pubis, that the 

 " marsu]_)ial bones " belong to that part of 

 the skeleton, and that they correspond with 

 the epipubis of certain amphibians and 

 reptiles. The pouch, it may be remarked, 

 exists in a rudimentary form in the males 

 of many Marsupials. 



The most salient feature in the life- 

 history of the J\Iarsui>ials is the imperfect 

 condition in which the young are born. 



The egg is no 



longer 



Fig. 60.— Ventral surface of 

 innominate bone of Kan- 

 garoo {Macrojms viajor). 

 X ^. «, Acetabulum ; ab, 

 acetabular border of ilium ; 

 is, iliac surface ; ?«., " mar- 

 supial" bone; pb, pubic completely 

 border ; pt, pectineal tu- 

 bercle ; s, symphysis ; si, 

 supra - iliac border ; 55, 

 sacral surface ; tftf, thy- 

 roid foramen ; ti, tuber- 

 osity of ischium. (From 

 Flower's Osti^ology. ) 



laid, as in the Mono- 

 tremes; but curiously 

 enough the ovum, 

 which has the small 

 size of that (if the 

 Eutheria, divides in- 

 at the 

 first division (as Mr. 

 (.'aldwell has shown), 

 and this develop- 

 mental feature may 



perhaps be looked 

 upon as a reminiscence of a former large- 

 yolked condition. The young when born 

 are small and nude ; the newly born young 

 is perhaps as large as the little finger, 

 ferred by the lips of the mother to the pouch, wliere they are 

 placed upon a teat. It is an interesting fact that they are 

 not merely imperfect foetuses, but that they are actual larvae. 

 They possess in fact at any rate one larval organ in the shape of 



Fig. 61. — Mammary foetus 

 of Kangaroo attached to 

 the teat. (Nat, size.) 

 (From Parker and Has- 

 well's Zoology,) 



of a large Kangaroo 

 The young are trans 



