SUBKIKGDOM VERTEBRATA. 



Fig. 69. 



ORDER UNGULATA. 



General Characteristics. The distinguishing feature 

 of this extensive order is that the toe-nails form hoofs. The 

 Families differ in almost every other respect* 



Ruminant Digestion. The food of Kuminants con- 

 sists of vegetable matter, little nutritious, and hence demanded 

 in large quantities. As they are in turn the food of carniv- 

 orous animals, and their only safety lies in flight, while 

 mastication is a work of time, they fill a large stomach- 

 reservoir by rapid grazing, re-chewing its contents in a place 

 of security. The stomach is divided into four compartments. 



The food passes without mas- 

 tication into the rumen (p) 9 

 next into the reticulum (b), 

 thence back through the 

 oesophagus (o) to the mouth, 

 where it is masticated ; then 

 down the oesophagus a second 

 time into the leaflet (/), and 

 thence into the caittette (c) or 

 true stomach. The mechanism 

 by which the food goes through 

 the same orifice at the bottom 

 of the oesophagus, at one time 

 into the rumen and at another 

 into the leaflet, may well create 

 surprise. The oesophagus is 

 continued below in a tube (c a), with a slit on the under 

 side whose lip-like edges shut water-tight, forming a passage 

 from the oesophagus to the leaflet. If, however, the mouth- 

 ful of food swallowed be large and solid, as it is when first 

 eaten, it distends the tube, and, separating the edges of the 

 slit, falls into the first stomach ; but if it be soft and pulpy, 

 as it is after being re-chewed, it does not force apart the edges 



Stomach of a Ruminant. 



* Those having the number of toes even are styled Artiodactyls, and odd, Perisso 

 dactyls. The Artiodactyls that chew the cud are termed Ruminants. 



