346 COMPARATIVE ZOOLOGY OF CHORDATES 



into two regions. The first of these, the proventri cuius, has 

 soft walls provided with glands. Next comes a hard- walled 

 gizzard, in which the food is crushed with the help of stones, 

 for the bird has no teeth and so cannot perform this function 

 in the mouth. 



In mammals, the stomach is simple except in a group of 

 the Ungulates called the Ruminants, where it is divided into 

 several parts. These animals " chew the cud," and their 

 stomach is modified in consequence. The food (grass) is 

 swallowed down (without being masticated) into the anterior 

 divisions of the stomach composed of the paunch and the 

 " honey-comb." When the animal ceases feeding, the food 

 is brought up to the mouth again and thoroughly chewed and 

 salivated. It then redescends to the other divisions of the 

 stomach, termed the maniplies and the abomasum. The latter 

 has glandular walls, and secretes digestive juice. 



The region between the intestine and the anus is short and 

 straight in the lower forms, and is called the rectum. It is 

 usually marked off from the intestine by the development of a 

 constriction, the ileo-colic sphincter, and by one or two blind 

 diverticula or coeca. In the Tetrapods the region between the 

 intestine and the anus becomes longer and coiled, and it becomes 

 possible to distinguish a so-called large intestine (on account 

 of its diameter) or colon which is coiled, from the terminal 

 straight rectum. The intestine proper is then called the small 

 intestine. The large intestine is concerned with the absorp- 

 tion of water from the non- digested remains of the food, a 

 function of importance for animals which inhabit dry land. 



The ccecum in mammals may be very large, as in the rabbit, 

 and this condition is common in herbivorous animals. The 

 ccecum contains a colony of bacteria whose function it is to 

 attack the cellulose of the food and to digest it. In other 

 forms the ccecum is reduced, and may be represented only by 

 its tip, the vermiform appendix, as in man. 



The anus primitively opens to the outside in conjunction 

 with the urino-genital ducts, forming a cloaca. This con- 

 dition is departed from in the higher bony fish (Teleostomes) 

 and in the higher mammals or Ditremata (Marsupials and 



