578 MAMMALS. 



on their walls which can be filled with fluid and closed by 

 sphincter muscles. 'The Camelidoe are unique among Mammals 

 in having oval, instead of circular red blood-corpuscles. The 

 placenta is diffuse. 

 Examples : — Camelus, ^ J§, the Arabian camel ( C. dromedarius) 

 has a dorsal hump of fat, the Bactrian camel (C bactrianus) 

 has two humps. The genus Auchenia, W\%, incliides the 

 llama, alpaca, huanaco, and vicugna of S. America, smaller 

 forms than the camels, and without humps. 

 Group 3. — Tragulina, comprising the family Tragulidse or Chevrotains. 

 These are small animals, "intermediate in their structure between 

 the Deer, the Camels, and the Pigs." There are four complete 

 toes on each foot, but the second and fifth are slender ; the third 

 and fourth metacarpals and metatarsals are fused in Tragulus, 

 free in the other genus Dorcatherium ; the fibula is complete. 

 There are no upper incisors, the upper canines are long and 

 pointed especially in the males, the lower canines are like 

 incisors, the dental formula is f^ff . The Chevrotains ruminate, 

 and the stomach is divided into three chambers. The placenta' 

 is diffuse. The chevrotains are often confusedly associated with 

 the musk-deer {Moschus) with which they have no special affini- 

 ties. 

 Species of Tragulus (smallest among living Ungidates) occur in Indo- 

 Malaya, India, and Ceylon ; one species of Dorcatherium, of aquatic pig- 

 like habits, is found on the west coast of Africa. 



Group 4. — Pecora or Cotylophora — the true Ruminants, including deer, 

 giraffes, cattle and sheep. Only the third and fourth digits are 

 complete, the fused second and third metacarpals and metatarsals 

 form "cannon-bones." Paired outgrowths of the frontal bones 

 are common, capped with horny sheaths in the Bovidas, deciduous 

 and restricted to the males in almost all Cervidse. There are no 

 upper incisors, and rarely upper canines ; there are three pairs of 

 lower incisors which bite against the hardened gum above, and 

 the lower canine resembles and is in the same series as the 

 incisors ; the typical dentition is -J^f. The stomach has four 

 distinct compartments, a psalterium or many-plies in addition to 

 the three which are present in Camels and Chevrotains. The 

 placenta is cotyledonary, the villi occuring on a number of 

 distinct patches. 

 The process of rumination or chewing the cud cannot be understood 

 without considering the complex stomach. It is divided into four 

 chambers, the paunch or rumen, the honeycomb bag or reticulum, the 

 many-plies or psalterium, the reed or abomasum. The swallowed food , 

 passes into the capacious paunch, the walls of which are beset with 

 close-set villi resembling velvet pile. After the food has been softened 

 in the paunch, it is regurgitated into the mouth where it is chewed over 

 again and mixed with more saliva. Swallowed a second time the food 

 passes not into the paunch, but along a muscular groove on the upper 

 wall of the globular honeycomb bag into the third chamber or many- 

 plies. The honeycomb bag owes its name to the hexagonal pattern 

 formed by the mucous membrane on its walls. The many-plies or 



