324 



COMPARATIVE ANATOMY. 



A curious fold of the skin of the abdomen is present to a greater or less degree 

 in Marsupials and in Echidna. This pouch ormarsupium serves to protect 

 the young, which are born in a very unripe condition, and thus renders possible 



FIG. 253. VARIOUS FORMS OF UTERI. A, B, C, D, diagrams showing the 

 different stages in the fusion of the Miillerian ducts : A, uterus bicornis ; B, 

 uterus simplex ; C, uterus duplex ; D, uterus bipartitus. E, female urinogenital 

 apparatus of Mustelina, with embryos (*, *) in the uterus. F, ditto of Hedgehog 

 (Erinaceus). 



Od, Fallopian tube ; lit, uterus ; Vg, vagina ; Ca, cervix uteri ; Ot, abdominal aper- 

 ture of Fallopian tube ; t, t, accessory sexual glands ; r, rectum ; Sug, urino- 

 genital sinus ; N, kidney ; Nn, adrenal ; Ur, ureter ; B, urinary bladder. 



a longer connection between the mother and embryo during lactation. The aper- 

 ture of the marsupial pouch opens anteriorly or posteriorly, according to the 

 mode of life of the animal, and is provided with a muscle capable of closing it. 



