102 TEXT-BOOK OF ZOOLOGY 



(e) The large quantity of food taken in calls into requisition a large 

 stomach for its reception and digestion, as well as of — 



(/) A long intestine — it is about twenty-two times as long as the 

 b dy — offering a large surface of absorption for the nutritious particles 

 of the food, which are only sparingly scattered throughout the whole 

 digestive mass (chyme). (Compare, on the contrary, the carnivora.) 



2. The nutritious elements of vegetable substances (starch, sugar, 

 albumin, etc.) are enclosed within hard coats of cellulose, which are 

 not dissolved by the digestive juices. In order that their enclosed 

 contents may be digested, these cellulose envelopes must be destroyed, 

 and to effect this the vegetable materials taken in as food require to be 

 crushed and ground up as finely as possible. (Compare, on the other 

 hand, the dog, which swallows a piece of meat thrown to it without 

 previously chewing it at all.) The grinding up of the food is effected by — 

 (a) A lateral grinding movement of the lower jaw. To this end the 

 articular heads, or condyles, of the lower jaw have the form of transversely- 

 placed rollers, turning in 

 corresponding sockets of 

 the temporal bones. 



(b) For the same pur- 

 pose the two rows of molars 

 in the upper jaw are placed 

 Row of Molabs in thb TJppbr Jaw of the Ox. farther apart than those of 



the lower jaw. 



(c) The crowns of the molars are broad, and their surfaces are raised 

 into blunt tubercles (compare with a millstone). 



(d) These tubercles have the form of crescent-shaped folds oj enamel 

 (selenodont), arranged in the longitudinal direction of the jaw, the 

 convexities of the crescents being turned inwards in the teeth of the 

 upper, and outwards in those of the lower, jaw (compare with rodents). 



(e) In order that the food may be thoroughly ground up, a large 

 grinding surface is necessary. Accordingly, the molars are both large 

 and numerous, six on each side above and below. 



(/) For the presence of such a number of large teeth large jaws are 

 required, which explains the elongated head of the ox. 



(g) There is a large gap or diastema between the incisor-like canines 

 and the molars in the lower jaws. 



(Compare the ox with the cat also in regard to incisors and molars, 

 length of jaws, equipment of feet with hoofs and claws respectively.) 



(h) The longer a man moves, and the more energetic his movements, 

 the more food is he obliged to take, in order to replace used-up force ; 

 the longer he remains at rest, the less force is used up, and consequently 



