64 



PLAN OF MAMMALIAN LIVER 



as this. Ill Fluduniji'f maculatus the two sections of the gut are 

 as nearly as possible equal in length, while in Pliascolaretos the 

 large intestine is consiclerahly longer than the small, the lengths 

 heing respectively 160 inches and 111 inches. It is common 

 among the ^Marsupials tmd also among the Eodents for these 

 proportions to exist, i.e. for the large intestine to be as long as, 

 or longer than, the small. But tliere are so many exceptions 

 that no general statements can be extracted from the facts. 



Some few details will be found in the systematic part of this 

 book. ill'. Chalmers Mitchell has brought forward some reasons 

 for associating a great length of larg-e intestine with an archaic 

 systematic position, in the birds at any rate. The facts here 

 briefly touched upon are not at variance with the extension of 

 such a view to the mammals. 



Appended to the alimentary tract are three glands or sets of 

 glands. Opening into the mouth cavity are the si(Urary glands, 



which are of enormous 

 size in Anteaters, and 

 small or absent in 

 AMiales. In their num- 

 ber and position these 

 glands are charactei-- 

 istic of mammals. Into 

 the intestine open the 

 ducts of the pancreas 

 and liver, two glands 

 which the mammals 

 share with lower verte- 

 brates. The form of 

 the liver is, however, 

 generally characteristic 

 of mammals. It is 

 divided as a rule into 

 a right and a left half, 



Fin. 42. — Diagrammatic ])laii of the liver of a Mammal 

 {posterior surface). l, Caudate lobe ; rf, cystic 

 fissure ; di\ ductus veuosus ; g, gall - bladder ; /c, 

 left central lobe ; U, left lateral lobe ; llf, left 

 lateral fissure ; p, portal vein entering transverse 

 fissun- ; re, right central lobe ; rl, right lateral lobe ; 

 rlf, right lateral fissure ; .s. Spigelian lobe ; m, uni- 

 liilical vein ; vc. post-caval vein. (After Flower 

 and Lydelvker. ) 



the line 

 umbilical 



of division 

 ligament, a 



being marked liy the insertion of the 

 vestige of the primitive ventral mesentery. Each half is again 

 commonly subdivided into central and lateral lobes. In addition 

 to these, two other divisions are often to be seen — the Spigelian 

 and the caudate lobe. The liver is less divided in Cetacea and 



