250 TAPIRS CHAP. 
Ungulate Phenacodus (see p. 202). In the next stage (an 
embryo of 25 mm.) the humerus has shghtly decreased in pro- 
portionate length, and has come to be more like that of 
Hipparion. In both of these embryos it should be noted that 
the ulna is complete and separate from the radius. In the 
second of the two it has more distinctly acquired the form which 
it will possess in the adult. The second metacarpal—one of the 
splint bones of the adult—is tipped with a small nodule of 
cartilage, which is clearly the representative of one or more of the 
phalanges belonging to that digit. 
Fam. 2. Tapiridae.—The Tapirs may be distinguished from 
the Horse and from the Rhinoceros tribe by a few characters, 
which are as follows :— 
The dentition is generally the full one of forty-four teeth. 
The premolars in the more ancient forms are unlike the molars, 
but like them in more recent forms. The molars of the upper 
jaw have two crests parallel and united by an outer crest. The 
fore-feet have four, the hind-feet three toes. 
The family is fully as ancient as that of the Equidae, but the 
specialisation of the toes never advances so far. The modern 
representatives of the order are, so far as the feet are concerned, 
in the condition of very early representatives of the equine stock. 
Nor do the teeth of the Tapirs ever reach the complicated pattern 
of that presented by at least the modern Horses, or indeed of the 
Palaeotheres. Apart from this it is not an easy matter to dis- 
tinguish accurately between these several families, including the 
Lophiodontidae, which, as already mentioned, is placed nearer to 
the Tapiridae than to the Palaeotheriidae. Indeed the differentia- 
tion of these two families, the Tapiridae and the Lophiodontidae, 
seems to be a matter of the greatest difficulty. The difficulty is 
well emphasised by the fact that naturalists disagree most 
profoundly as to the relations of various genera of extinct Tapir- 
like animals. For Mr. Lydekker the genus Lophiodon includes 
also the American genera Jsectolophus and Systemodon, which are 
placed by Zittel in the sub-family Tapirinae as opposed to 
Lophiodontinae, which contains Lophiodon and Helaletes. The 
existing Tapirs can be differentiated from the existing Horses with 
great ease, as the following account of the existing genera will 
show. 
The genus Zapirus is now met with only in South and 
