HISTORY OF THE ARTIODACTYLA 387 



the modern genera. In the true camels (Camelus) the first 

 and second upper incisors have been lost, but the third re- 

 mains as a large, sharp-pointed tooth, as are also the upper 

 canine and first premolar ; thus there are three pointed, spike- 

 like teeth in a row, with spaces between them, constituting 

 with the lower canine a very effective lacerating apparatus. 

 Behind the first premolar is a long gap, the second being sup- 

 pressed ; the third and fourth are grinding teeth, but unusually 

 small. The molars are selenodont and high-crowned, though 

 not extremely hypsodont. The lower incisors are large and 

 shovel-shaped, the canine large and erect and there are but two 

 lower premolars. The dental formula thus is : i^, c\, p I, m f . 

 The skull is long, with the facial region much and abruptly 

 narrowed, which gives a triangular appearance to the head when 

 seen from above ; the orbit is completely encircled with bone 

 and the sagittal and occipital crests are very prominent. The 

 tympanic bulla? are large and filled with spongy bone. The 

 condyle of the lower jaw is hemispherical and not, as it is in 

 most ungulates, semicylindrical, and a curious, hook-like 

 angulation is on the posterior border of the bone. The neck 

 is very long, and the vertebrae have the exceptional peculiarity 

 that the canal for the vertebral artery runs through the side of 

 the neural arch, instead of perforating the transverse process, 

 and thus is invisible externally ; the odontoid process of the 

 axis is spout-like. The legs and feet are very long ; the 

 humerus has a double bicipital groove and the fore-arm bones 

 are coossified, and the ulna is so reduced that the radius carries 

 the whole weight ; in the lower hind leg the tibia supports the 

 weight, and of the fibula only the lower end remains as the 

 malleolar bone. There are but two digits in each foot, the 

 third and fourth, the metapodials of which have coalesced 

 to form a cannon-bone, which differs from that of the true 

 ruminants, or Pecora, in the curious way in which the lower 

 ends, separated by a A-shaped notch, diverge from each other, 

 and by the fact that the keels of the lower articular surfaces 



