. RUMINANT QUADRUPEDS. 505 



vorous mammalia, but of a single bone only, 

 termed the cannon bone. In the early periods of 

 ossification, however, they each consisted of two 

 slender bones, lying close and parallel to each 

 other ; but afterwards united by an ossific depo- 

 sition, which fills up the interval between them, 

 and leaves behind no trace of suture.* In pro- 

 portion as the young animal acquires strength, 

 the union of these two bones becomes still more 

 intimate by the absorption of the partition which 

 separated their cavities ; so that ultimately they 

 constitute but one cylinder, with a single central 

 cavity, which is occupied by marrow. 



The cannon bone is much elongated, both in 

 the fore and hind extremity ; so that the carpus 

 and tarsus, which are the commencements of the 

 real feet, are raised considerably above the 

 ground. It is a common mistake, arising from 

 the height of these joints, and the names they 

 bear in ordinary language, to consider them as 

 the knees of the animal. The slightest inspec- 

 tion of the skeleton will be sufficient to show 

 that what is called the knee in the fore leg is 

 properly the wrist ; and in the hind leg, the part 

 so misnamed is really the heel. Thus the foot, 

 especially in the posterior extremity, is of great 

 length ; a structure which is evidently intended 



* The observations which establish this fact are detailed by G. 

 St. Hilaire, in a paper in the " Memoires du Museum," x. 173. 



