7oo 



MAMMALIA. 



placenta is cotyledonary, the villi occurring on a number of dis- 

 tinct 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 orTumen, 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. Swal- 

 lowed 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 chamberormany-plies. The honeycomb- bag 

 owes its name to the hexagonal pattern formed by 

 the mucous membrane on its walls. The many- 

 plies or psalterium is a filter, its lining membrane 

 being raised into numerous leaf-like folds covered 

 with papillae. Along these the food passes to 

 the reed, which secretes the gastric juice. 

 Cervidse — the widely distributed deer, absent 

 only from the Ethiopian and Australian 

 regions. The second and fifth digits 

 are usually represented, often along with 

 the distal parts of the corresponding 

 metacarpals and metatarsals. The upper 

 canines are usually present in both sexes. 

 The horns, if present, are antlers, de- 

 ciduous, and usually confined to the males. 

 In the reindeer they are possessed by 

 both sexes. They are outgrowths of 

 the frontal bones, are covered during 

 growth by vascular skin — the velvet — 

 and attain each year to a certain limit of 

 growth. After the breeding season the 

 blood supply ceases, the velvet dies off, 

 and an annular absorption occurs near 

 the base. Then the antlers are shed, 

 leaving a stump, from which a fresh but 

 larger growth takes place in the next 

 year. The earliest (Lower Miocene) deer had no antlers, thus 

 resembling young stags of the first year ; the Middle Miocene 

 deer had simple antlers, with not more than two branches, thus 

 resembling two-year-old stags. Thus there is a parallelism 

 between the history of the race and the individual development. 

 Examples. — Cervus, most Old World deer; Rangifer, the reindeer; 

 Alces, the elk or moose ; Capreolus, the roe-deer ; Hydropotes, 

 the water-deer, without antlers ; Moschus, the musk-deer, 

 without antlers, with long sharp upper canines in the males, 

 with large musk glands. 



Fig. 307. — Side view 

 of calf's fore-leg. 



k., Distal end of humerus ; 

 «., olecranon process of 

 ulna; r., radius; mc.3, 

 4, metacarpals 3 and 4 

 fused to form cannon 

 bone ; mc.5, fifth meta- 

 carpal ; «., nodule. 



