PELVIC ARCH 



121 



In Whales, in which hind-limbs are wanting, paired rudiments of the 

 ischio-pubic region of the pelvis are present. They are unconnected with 

 one another and with the vertebral column. 



In Monotremes and Marsupials of both sexes, two strong so- 

 called "marsupial bones" (Fig. 100) arise from the anterior 

 border of the pubes, right and left of the middle line, and extend 

 forward in a straight or oblique direction embedded in the 



Tul.H.p , 



+ -* Ti 



FIG. 100. PELVIS OF A, Echidna hystrix (ADULT), AND B, Didelphys azarce 

 (F(ETUS, 5'5 CM IN LENGTH). (From the ventral side.) 



Ep, epipubis ("marsupial bone") ; P, pubis ; Sy, ischiopubic symphysis ; Js, 

 ischium ; J, ilium ; Fobt, obturator foramen ; Tub.il. p, ilio-pectineal tubercle ; 

 Lg and Lgt, ligament between the pubis and epipubis ; **, cartilaginous 

 apophysis at the anterior end of the epipubis. 



In Fig. A, t*, t, tt, ilio- and ischio-pubic sutures ; Z, process on the anterior 

 border of the pubis ; GH, articulation between the pubis and epipubis ; Tb, 

 cartilaginous tuber ischii. 



In Fig. B, b, 6 1 , cartilaginous base of the epipubis, continuous with the inter- 

 pubic cartilage at t ; *, *t, ischio-pubic and ischio-iliac suture. 



body .-walls. They form an integral part 'of the pelvis, and in the 

 embryo are seen to be in direct connection with its cartilaginous 

 symphysis ; but later on articulations are formed between them 

 and the pubes. There can be no doubt that these structures are 

 the homologues of the epipubis of lower Vertebrates, which has 

 been retained in non-placental Mammals in order to serve as a sup- 

 port for the abdominal walls in connection with the marsupial 

 pouch (p. 28). 



