Via 



ilia: Visceral System 



649 



Y(Jlw) 



y a 



Fig. 491. Urinogenital organs of marsupials. (A) A young opossum {Didelphys 

 dorsigera). (B) Phalangista vulpina. (b) Urinary bladder; (67) cloaca; (g) clitoris; 

 (n) kidney; (Od) Fallopian tube; (0/ (Fim)) fimbriated abdominal opening of ovi- 

 duct; (Ov) ovary; (r) rectum; (r 1 ) anus; (Sp) septum; {Sug) urinogenital sinus; 

 (Ur) ureter; (Ul) uterus; (Ut 1 ) openings of uteri into vaginal cecum; (Vg) vagina; 

 (Vg 1 ) vaginal opening into urinogenital sinus; (VgB) vaginal cecum; (t) junction 

 of uterus and vagina; (*) rectal gland. (Courtesy, Wiedersheim : "Grundriss der 

 vergleicbenden Anatomie der Wirbeltiere," Jena, Gustav Fischer.) 



divides the vaginal chamber and its cecum. In some kangaroos the 

 vaginal cecum grows backward and acquires a median opening into 

 the urinogenital sinus, the extraordinary result being three vaginal 

 passages extending between the urinogenital sinus and the two uteri. 



The deficiencies of the internal uterine arrangements in marsupials 

 are compensated for by provision for continuation of maternal care 

 and feeding after birth of the young. The minute and helpless newborn 

 fetus is transferred to an external posteroventral pouch, the marsu- 

 pium, formed by a fold of abdominal skin (Fig. 539). The pouch is 

 supported by a pair of elongated epipubic or marsupial bones which 

 project forward from the anterior bones, pubes, of the pelvic girdle. 

 The epipubes, like the pubes, are cartilage-bones. The mammary 

 glands are on the abdominal wall within the pouch. 



The marsupium is present only in the female. In most cases it opens 

 forward. In the bandicoots (Perameles and Chaeropus) and the marsu- 

 pial mole (Notoryctes) it opens backward. The reversal in the direction 

 of the opening is a very fortunate adaptation to the burrowing habit 



