XI RUMINATION 281 
in the upper jaw, and very usually there are none. As a 
general rule the third and fourth metacarpals and metatarsals 
become united to form a cannon bone. To this there is but one 
exception, the African Hyomoschus. Moreover, the second and 
fifth digits are nearly always rudimentary, and may practically 
disappear altogether. Here again the Tragulidae are an excep- 
tion. The Ruminantia are so-called on account of the fact that 
they “ruminate,’ that is, after the food has been rapidly 
Fic. 146.—Stomach of Ruminant opened to show the internal structure. @, Oesophagus ; 
b, rumen; c¢, reticulum; d, psalterium; e, abomasum; jf, duodenum. (After 
Flower and Lydekker. ) 
swallowed, it is forced back up the gullet and more thoroughly 
masticated. Associated with this is a complex stomach, which 
is divided into several compartments. This stomach has at least 
three compartments, as in the Tragulidae ; but it has usually four. 
Its characters are illustrated in Fig. 146. The majority of the 
Selenodontia possess horns, which are partly formed of solid 
protuberances of the frontal bones. In the Giraffe they are 
somewhat different. 
This group may be divided into—A. TRAGULINA, Chevro- 
tains; B. TyLopopA, Camels, Lamas; and C. PEcora, Deer, Ante- 
lopes, Oxen, Giraffes, Goats, Sheep. 
A. TRAGULINA. 
As the Tragulina are undoubtedly the most ancient of the 
Selenodontia it will be logical to commence with an account 
of them. 
