

CHORDATA 



most of the common characters enumerated above have been independently 

 acquired so that the uniformity in appearance is in great part the result of 

 convergence. 



Sub Order I. PERISSODACTYLA. Molars and premolars (with more 

 or less pronounced enamel folds) of equal size; predominant development of the 

 middle toe, the others reduced to different degrees. TAPIRID^;, fore feet four- 

 toed, hind feet three-toed; teeth '}, \ ;j ;S ; nose elongate into a proboscis. Tapirus, 

 tapirs, tropical America and India. RHINOCEROTUXE, three toes on all feet, 

 teeth I 1 , 1 ,':;; one or two horns on the nasal bones; skin thick, hairless (hence 

 these- were formerly united with elephants as Pachydermata). Rhinoceros,- 

 single horn, India; Ci'mturliiiiits (Asia), Atdodus (Africa), two horns. EQUID^, 

 a single functional toe (fig. 615, C); teeth |i-|-|; Equus caballus,* horse, a native 

 of Asia; E. asinus, ass; E. Zebra. 



Sub Order II. ARTIODACTYLA. Besides the features of the feet, these 

 have the three or four premolars, smaller than the molars. Species much more 

 numerous than of perissodactyles. Section I, NON-RUMINANTIA (Buno- 

 dontia); omnivorous and have a bunodont dentition, r^ll!;], the canines fre- 

 quently developed into tusks; stomach usually simple, but occasionally divided 

 into three chambers (Dicotyles, Hippopotamus}, although rumination does not 

 occur. The leg skeleton is little modified (fig. 615, D], ulna and fibula not 

 reduced, metacarpals and metatarsals separate. HIPPOPOTAMID.E; all four toes 

 reach the ground; skin thick ('pachyderm'), body heavy; African. Hippopota- 

 mus. SI-ID.E; two functional toes, skin with bristles, snout proboscis-like. 

 Sus scrofa, swine; Dicotyles,* peccaric3. 



FIG. 6r6.--Stomach of sheep (after Carus and Otto), a, abomasum (true stomach) ; 

 o, omasum (manyplies) ; re, reticulum (honeycomb); ru, rumen (paunch). 



Section II. RUMINANTIA (Pecora); teeth and stomach adapted to the 

 exclusively herbivorous diet. The stomach (fig. 616) is divided into two per- 

 ms, each again subdivided. The first of these, the rumen, or paunch (nt), 

 eceives the food as it is eaten; then at a time of quiet it is regurgitated into the 

 i and -round by the molars ('chewing the cud'). It then passes back, 

 ime into the second division, the honeycomb, or retindum (re), thence to 

 urn-pin (psalterium) or omasus (o), and lastly to the abomasus, or true 

 Usually canines and incisors of upper jaw degenerate; incisors 

 .ower jaw strong and the canines have form and position of incisors 



