XIII 



PHYLUM CHORDATA 



541 



A coecum situated at the junction of the large and small intes- 

 tines is usually present, but varies greatly in extent in the different 



orders and families. 



It is much larger in 



vegetable feeding 



than in carnivor- 

 ous forms, and 



among the former 



it is those that 



have a simple 



stomach, such as 



the Rabbit, that 



have the largest 



caecum. Hyrax dif- 



ers from all the 



rest of the class in 



having a pair of 



supplementary 



coeca situated some 



distance down the 



large intestine. A 



coecum is absent in 



the Sloths, some 



Cetacea, and a few 



Carnivora. 



The Prototheria resemble Reptiles, Birds, and Amphibia, and 



differ from other Mammals in the presence of a cloaca, into which 



not only the rectum, but the urinary and genital ducts open. In 



the Marsupials a com- 

 mon sphincter muscle 

 surrounds both anal 

 and urino-genital aper- 

 tures ; in nearly all the 

 Eutheria the apertures 

 are distinct, and separ- 

 ated from one another 

 by a considerable space 

 the perinceum. 



The liver (Fig. 1132) 

 consists of two parts or 

 main divisions, right 

 and left, incompletely 

 separated from one 

 another by a fissure 

 termed umbilical owing 

 to its marking the 

 position of the foetal 



FIG. 1131. Diagrammatic section of thestomachof the Porpoise. 

 a, ossophagus ; b, left or cardiac compartment ; c, middle com- 

 partment ; d and e, the two divisions of the right, or pyloric 

 compartment ; /, pylorus ; g, duodenum, dilated at its com- 

 mencement ; h. bile-duct. (After Flower and Lydekker). 



II j 



FIG. 1132. Diagrammatic plan of the liver of a Mammal 

 (posterior surface), c. caudate lobe ; c/. cystic fissure ; dc. 

 ductus venosus ; g. gall-bladder ; Ic. left central lobe ; 

 II. left lateral lobe ; llf. left lateral fissure ; p. portal vein 

 entering transverse fissure ; re. right central lobe ; rl. right 

 lateral lobe ; rif. right lateral fissure j s. Spigelian lobe ; 

 u. umbilical vein ; re, post-caval. (After Flower and 

 Lydekker.) 



