COMPARATIVE ANATOMY, 



In the proper mollusca, besides the sto- 

 mach, which has been already noticed, 

 there is an intestine, seldom of considera- 

 ble length, making some turns in its 

 course ; it passes in all the acephalous 

 mollusca through the heart. 



The intestinal canal of insects varies 

 very much in the different genera and 

 species. It may be stated, on the whole, 

 that a long and complicated intestinal tube 

 denotes that the insect feeds on vegeta- 

 bles ; while the contrary characters indi- 

 cate animal food. 



Great difference is found, in some in- 

 stances, between the larva and the per- 

 fect insect. The voracious larvae of bee- 

 tles (scarabaei) and butterflies, have intes- 

 tines ten times as large as the winged in- 

 sects which are produced from them. 



In the dragon-fly (libellula,) which is 

 very carnivorous, the intestine is not long- 

 er than the body. There is a small but 

 muscular stomach. 



The orthoptera (which class contains 

 the locusts, &c. well known for their de- 

 structive powers) have a long and com- 

 plicated alimentary apparatus. They have 

 first a membranous stomach. This is suc- 

 ceeded by another cavity covered inter- 

 nally with scales or teeth, and possessing 

 a very thick muscular coat ; in short, a 

 true gizzard. Round the end of this the 

 cjecal processes are attached. There is, 

 lastly, an intestinal canal, differing in 

 length and diameter. 



The alimentary canal runs straight 

 along the body in the erustacea, and is 

 uniform in its dimensions, excepting the 

 stomach. 



ON THE LIVEE, SPLEEN, AND OMEN- 

 TLM. 



The spleen and omentum seem to be 

 less constantly found in the animal 

 kingdom than the liver, and to be in a 

 manner subservient to the latter viscus ; 

 which, on the contrary, exists in every 

 class and order of animals that is pro- 

 vided with a heart and circulating sys- 

 tem. 



It deserves to be remarked here, as a 

 peculiarity of the liver of some four- 

 footed mammalia, which live in or about 

 the sea, namely, the polar bear and some 

 seals, that it s'eems to possess some poi- 

 sonous or noxious qualities when employ- 

 ed for food. Ileernskerk's companions 

 experienced this, in the former instance, 

 at Nova Zemlia ; and Lord Anson's squad- 

 ron, in the latter, on the coast of Pata- 

 gonia. 



The liver of mammalia is in general di- 

 vided into more numerous lobes ; and the 

 divisions are carried deeper into its sub- 

 stance than in the human subject. This 

 is particularly the case in the carnivora, 

 where the divisions of the lobes extend 

 through the whole mass. But the utility, 

 which Munro has assigned to this struc- 

 ture, viz. that of its allowing the parts to 

 yield and glide on each other in the rapid 

 motions of the animal, carries very little 

 plausibility with it. " Essay on Compara- 

 tive Anatomy," p. 11. 



In many animals of this class, as the 

 horse, the ruminantia, the pachydermata, 

 and whales, the liver is not more divided 

 than in man. 



The ductus coledochus forms a pouch 

 between the coats of the intestine, for re- 

 ceiving the pancreatic duct, in the cat and 

 elephant. 



AH the quadrumana, carnivora, and 

 edentata, have a gall-bladder. 



Many rodentia, particularly among the 

 rats, want it. The tardigrada ; the ele- 

 phant, rhinoceros, and pecari, among the 

 pachydermata ; the genus cervus and ca- 

 melus, among the ruminating animals ; 

 the solipeda; the trichechus and porpoise 

 also want this part. It does not exist in 

 the ostrich and parrot ; but is found in 

 all the reptiles. Cuvier thinks that it be- 

 longs particularly to carnivorous animals ; 

 that it is connected with their habit of 

 long fasting ; and serves as a reservoir for 

 the bile. 



All the mammalia which want it, ex- 

 cept the porpoise, are vegetable eaters: 

 and most reptiles, which universally pos- 

 sess it, live on animal food. 



The liver of birds is divided into two 

 equal lobes. The hepatic duct opens se- 

 parately from the cystic ; and its termina- 

 tion is generally, but not always, preced- 

 ed by one or more pancreatic ducts, and 

 followed by that of the cystic duct. 



The fundus of the gall-bladder receives 

 branches from the hepatic duct (" ductus 

 hepaticystici") ; but the tube sometimes 

 unites with the cystic, as in the duck. 



Some fishes, which are most destitute 

 of fat in the rest of their body, have an 

 abundance of oil in their liver, as, for in- 

 stance, the skate and cod. 



The spleen gradually diminishes in size 

 from the mammalia to fishes. In the por- 

 poise there are several small spleens, sup- 

 plied from the arteries of the first sto- 

 mach. It is always attached to the first, 

 when there are several stomachs. 



In birds it is always near the bulbus 

 glaudulosus, but does not lie constantly 



