586 



UNGTJLATA. 



folds leading from it to the psalterium. The lips of these folds can be 

 approximated so as to convert the gi-oove into a canal leading from the 

 oesophagus to the psalterium. The food when first swallowed passes into the 

 rumen and reticulum and remains there, mixed with swallowed saliva 

 until the animal has eaten what it requires. It then lies down to chew the 

 cud or ruminate. The first part of this process is akin to vomiting, 

 portions of the swallowed food being successively regurgitated into the 

 mouth, by a contraction of the diaphragm and abdominal muscles and a 

 reversed peristalsis of the oesophageal muscles. In the mouth it is 

 thoroughly mas- 

 ticated and then 

 again swal- 

 lowed. But now 

 the finely tri- 

 turated food 

 does not stay in 

 the paunch but 



passing along 

 the groove, the 



lips of which 



may be approxi- 

 mated, it enters 



the psalteririm 



through which it 



passes into the 



abomasum, 



where it is sub- 

 mitted to the 



action of the 



gasti'ic juices. 



In the Tragu- 



lidae and the 



Camelidae the 



stomach is very 



similar in its 



main features, 



but the psalter- 

 ium is reduced 



or absent. The 



placenta is 



generally coty- 



ledonary, i.e. the villi of the chorion are concentrated into a number 



of bunches or cotyledons, the intermediate portions being devoid of 



papillae. 



The Ruminantia comprise the Camelidae, Tragulidae, and Pecora. 



Fam. 9. Camelidae (Tylopoda). Without horns ; i^ cip j^wf; 

 the dentition is complete in some of the extinct, but reduced in the liv- 

 ing ; grinders selenodont, hypsodont. Arches of the cervical vertebrae 

 perforated by the vertebrarterial canal as in Macrauchenidae ; orbit 

 enclosed, tympanic bullae filled with spongy bone. Ulna reduced and 

 ankylosed to radius, fibula represented only by its distal end, the malleolar 

 bone, which is articulated to the lower end of the tibia and to the cal- 

 caneum. Trapezoid and magnum, cuboid and navicular distinct, cunei- 

 forms 2 and 3 fused ; feet tetra- or didactyle, outer toes absent in recent 



Fig. 306. — A stomach of a sheep, B of Tragutus. oe oesophagus, 

 Ru rumen, Ret reticulum, Ps psalterium, A, Ab abomasum, Du 

 duodenum, Py pylorus (from Huxley). 



