o74 



ZOOLOGY 



SECT. 



The liver (Fig. 1201) 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 left lateral (II.) and left central (Ic.) lobes are 



distinguishable. When 

 a gall-bladder is pre- 

 sent, as is the case in 

 the majority of Mam- 

 mals, 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 

 passes out, crosses the 

 right centra] lobe near 

 the anterior border. 

 The postcaval lies in 

 contact with, or em- 

 bedded in, the right 

 lateral lobe near its 

 anterior border, and, 

 given off from this lobe between the postcaval and the portal 

 fissure, is a small lobe, of varying extent — the Spigelian. The 

 term caudate lobe is applied to a process of the right lateral 

 lobe, of considerable extent in most Mammals, having the post- 

 caval vein in intimate relation to it, and often closely applied to 

 the kidney. A gall-bladder is usually present, but is absent in 

 the Cetacea, the Perissodactyle Ungulata, the Hyracoidea, and 

 some Rodents. 



Vascular System.— The blood of Mammals is warm, having a 

 temperature always of from 35° to 40° C. The red corpuscles are 

 non-nucleated : in form they are most usually biconcave discs, 

 always circular in outline except in the Camelidse, in which 

 most of them are elliptical. The lymphatic system of vessels is 

 very highly developed, ramifying richly throughout all parts of 

 the body. In the course of this system occur numerous lymphatic 

 glands. The special part of the lymphatic system of vessels 

 {lacteals) which ramify in the wall of the intestine and absorb 

 the fatty matters of the food, combine with the lymphatic vessels 

 from the hind-limbs and body to form a receptacle — the recepta- 

 culum chyli — from which a tube — the thoracic duct — which may 



Fio. 1201. — Diagrammatic plan of the liver of a Mammal 

 (posterior surface), c. caudate lobe ; cf. cystic fissure ; dv. 

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

 U. left lateral lube ; Uf. left lateral fissure ; p. portal vein 

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

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

 v.. umbilical vein ; fc, postcaval. (After Flower and 

 Lydekker.) 



