6 4 



PLAN OF MAMMALIAN LIVER 



as this. In Plialanger maculatus the two sections of the gut are 

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

 large intestine is considerably longer than the small, the lengths 

 being respectively 160 inches and 111 inches. It is common 

 among the Marsupials and also among the Rodents for these 

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

 or longer than, the small. But there 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. Mr. Chalmers Mitchell has brought forward some reasons 

 for associating a great length of large 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 salivary glands, 



which are of enormous 

 size in Anteaters, and 

 small or absent in 

 Whales. In their num- 

 ber and position these 

 glands are character- 

 istic of mammals. Into 

 the intestine open the 

 ducts of the pancreas 

 and liver, two glands 

 > which the mammals 



u share with lower verte- 



brates. The form of 



FIG. 42. Diagrammatic plan of the liver of a Mammal . , 



(posterior surface). c, Caudate lobe; cf, cystic the Mer IS, however, 

 fissure; dv, ductus venosus ; g, gall-bladder; Ic, generally characteristic 

 left central lobe ; If, left lateral lobe ; llf, left * 

 lateral fissure ; p, portal vein entering transverse OI mammals. It IS 

 fissure ; re, right central lobe ; rl, right lateral lobe ; (Jjyj(J e( J as y rule into 

 rlfj right lateral fissure ; s, Spigelian lobe ; u, um- 

 bilical vein ; vc, post-caval vein. (After Flower a right and a left half, 

 andLydekker.) the Hne of di v i s i on 



being marked by the insertion of the umbilical ligament, a 

 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 



