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 
gy 
Fic. 406.—Side view of sheep’s skull. 
PMX., Premaxilla; JZX., maxilla; VA., nasal; /., Jugal; Z., lachrymal; 
FR., frontal; PA., parietal; SQ., squamosal; CO., condyle; PP., 
paroccipital process. 
Camelidz are unique among Mammals in having oval instead of 
circular red blood corpuscles. The placenta is diffuse. 
Examples.—Camelus, 8, the Arabian camel (C. dromedarius) 
has a dorsal hump of fat, the Bactrian camel (C. dactrianus) 
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 Azchenia, fae 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- 
