556 



ZOOLOGY 



SECT. 



(Fig. 1212) the oesophagus (a) opens into a spacious paunch (b), 

 the cardiac compartment of the stomach, with a smooth, thick, 

 mucous membrane. This is followed by a second chamber (c), of 

 considerably smaller dimensions, with a glandular mucous mem- 

 brane, which is thrown into a number of complex folds. A long 

 and narrow third, or pyloric, compartment (d, e) follows upon 

 this, terminating in a constricted pyloric aperture, beyond which 

 the beginning of the intestine is dilated into a bulb. 



A caecum, 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 carnivorous forms, and among the former it is those that have 

 a simple stomach, such as the Rabbit, that have the largest caecum. 

 Hyrax differs from all the rest of the class in having a pair of 



supplementary caeca 

 situated some distance 

 down the large intes- 

 tine. A caecum is 

 absent in the Sloths, 

 some Cetacea, and a 

 few Carnivora. 



The Prototheria re- 

 semble Reptiles, Birds, 

 and Amphibia, and 

 differ from other 

 Mammals, in the pre- 



cf J sence of a cloaca, into 



which not only the 



FIG. 1213. Diagrammatic plan of the liver of a Mammal rectum but the Urinary 



(posterior surface), c. caudate lobe; cf. cystic fissure; o 1lr l o-pnital rlnrts nr>pn 



ffe. ductus venosus ; g. gall-bladder ; fc. left central lobe ; al " lb . P en ' 



II. left lateral lobe ; llf. left lateral fissure ; p. portal vein In the Marsupials 



common sphincter 

 muscle surrounds both 

 anal and urinogenital 

 apertures and in the female there is a definite cloaca ; in nearly all 

 the Eutheria the apertures are distinct, and separated from one 

 another by a considerable space the perinceum. 



The liver (Fig. 1213) consists of two parts or main divisions, 

 right and left, incompletely separated from one another by a fissure 

 termed the umbilical, owing to its marking the position of the foetal 

 umbilical vein. Typically each of these main divisions is divided 

 by a fissure into two parts, so that right lateral (rl.) and right central 

 (re.) and kft lateral (II.) and left central (k.) lobes are distinguishable. 

 When a gall-bladder is present, as is the case in the majority of 

 Mammals, it is attached to, or embedded in, the right central lobe. 

 A fissure, the portal, through which the portal vein and hepatic 

 artery pass into the substance of the liver, and the hepatic vein 



llf 



. . 



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

 right lateral lobe ; rlf. right lateral fissure ; s. Spigelian 

 lobe ; u. umbilical vein ; vc. post-caval. (After Flower 

 and Lydekker.) 



a 



