756 



MAMMALIA. 



are long, with only the third and fourth digits developed ; the 

 two metacarpals and metatarsals are united for the greater part 

 of their length, but there is a deep distal cleft ; the tips of the 

 digits have very incomplete hoofs, and the animals walk on a 

 broad pad of skin surrounding the middle phalanges. The 

 femur is long and vertical, and the knee is low down. Of the 

 three upper incisors only one persists in adult life, as an isolated 

 sharp tooth, those of the lower jaw are long and slope forwards. 

 There are canines both above and below. The molars are 

 selenodont. The stomach shows a complex rumen with glandular 



water-cells," a tubular psalterium, and an abomasum. The 



FIG. 406. Side view of sheep's skull. 



PMX. , Premaxilla ; MX., maxilla ; NA., nasal ; /., Jugal ; L., lachrymal ; 

 FR. t frontal; PA., parietal; SQ., squamosal ; CO., condyle ; PP., 

 paroccipital process. 



Camelidae are unique among Mammals in having oval instead of 



circular red blood corpuscles. The placenta is diffuse. 



Examples. Camelus , x 3 , the Arabian camel (C. dromedarius} 



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



has two humps. The camel has a very small area of visible 



perspiration on the back of the neck, and seems to have a 



somewhat variable body-temperature, two associated facts which 



may be adapted to conserving the animal's water-supply in arid 



countries. The genus Auchenia, ; , includes the llama, 

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

 than the camels, and without humps. 



Group 3. Tragulina or Chevrotains, 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 meta- 



