MAMMALIA. 



467 



than that of the lower types. The main point to notice is the gradual 

 separation of rectum and urogenital canal from a common cloaca, a 

 process akin to that seen in the female. 



Skeleton. — The skeleton in Mammalia is almost en- 

 tirely bony, but the bones mostly have epiphyses. These, 

 as already explained in the general features of Vertebrata 

 (page 413), are produced by the persistence of a thin layer 

 of unossified cartilage during life. 



Fig. 323. ^Diagram of Mammalian Female Urogenital 

 Organs. 



I, The Prototheria. 2, The Metatheria. 3, The Eutherian bipartite uterus. 4, The 

 Eutherian bicornuate uterus. 5, The Eutherian simple uterus. 



The general characters of the mammalian skull have 

 been noticed in the rabbit. The facial and cranial por- 

 tions are completely joined together. Specially interesting 

 are the parts connected with the suspensorium and the ear- 

 ossicles. 



In Sauropsida the quadrate suspends the mandible, but 

 in the mammals the squamosal bone grows down to meet 



