LIVEK OF MAMMALIA. 48] 



by a rather wide hepatic duct to the duodenum. I conclude, 

 therefore, that the absence of the gall-bladder is the rule, or normal 

 condition ; and that the Giraffe in this respect, as in the structure 

 of its horns, has a nearer affinity to the Deer than to the Ante- 

 lopes. In these and all hollow-horned Ruminants, a gall-bladder 

 is present; as it is, also, in Moschus and Tragulus. In the Came- 

 lidcB the gall-bladder is absent as in the Cervidce. A like absence 

 characterises all Perissodactyles, and suggests some relationship 

 with the small capacity and simple structure of the stomach com- 

 pared with the quantity of food taken, and with the rapid and 

 continuous transit of the gastric contents through the small intes- 



o o 



tines to the enormous cascal and colonic receptacles where diges- 

 tion is finally completed. But the somewhat capricious appear- 

 ance of the gall-bladder in vegetarian Mammals discourages such 

 attempts to physiologise. Thus the Hog, e.g. w r ith the simple 

 stomach has the gall-bladder, while the Peccary, with a complex 

 one, has it not. 



The liver, fig. 308, r, r, closely retains the mammalian type of 

 the organ in Monotremes. Four lobes may be distinguished in 

 the Echidna : the principal or cystic lobe receives the suspensory 

 ligament in a fissure ; the large gall-bladder is placed a little to 

 the right of this ; the left lobe occupies the left hypochondrium ; 

 the Spigelian lobule is of moderate size ; it is an appendage of 

 the right lobe. The liver presents nearly the same form in the 

 Ornithorhynchus, which has likewise a large gall-bladder, ib. s. 

 There are three hepatic ducts in the Echidna which join the 

 cystic, and the common canal terminates in the duodenum rather 

 more than an inch from the pylorus. In the Ornithorhynchus 

 the two chief hepatic ducts join the cystic near the neck of the 

 bladder ; the third hepatic joins a more distant part of the cystic ; 

 the ductus choledochus receives the pancreatic duct about 9 lines 

 before its termination, as in the Marsupials, w r here its coats are 

 thickened and glandular, and opens into the duodenum about 8 

 lines from the pylorus. 



The liver is subdivided into many lobes in all the Marsupial 

 genera. It is relatively largest in the burrowing Wombat and 



O v O 



carnivorous Dasyure ; relatively smallest in the graminivorous 

 Kangaroo, in which it is situated, as in the placental Ruminants, 

 entirely to the right of the mesial plane. The small or Spigelian 

 lobe, which fits into the lesser curve of the stomach, is given 

 off from the left lobe of the liver in the Kangaroos, but from 

 the right in most other Marsupials ; the difference just noticed 

 in the Kangaroo depends on the peculiar disposition of its re- 

 VOL. III. I I 



