530 UNGULATES. 



slightly diverging from the alveoli : they are opposed above by a 

 callous gum, and are thereby better adapted for cropping or tearing 

 the herbage and foliage on which the Ruminants subsist. 



The true molars, three in number on each side of both jaws, 

 are constant ; the premolars are subject to some variety. They 

 are essentially four in number in each series ; but the first, in 

 the true Ruminants, is feebly and transitorily represented by a 

 rudimental matrix developed in the primitive dental groove at a 

 short distance in advance of the second deciduous molar, and has 

 no successor. The second deciduous molar, or that which is 

 essentially such, is developed as the first of the functional molar 

 series of the immature animal (PI. 133, fig. 4, d 1), and is 

 displaced by the tooth, marked ^ 1 in figs. I & 4, which is the 

 first of the permanent molar series, and is here indicated and 

 described as the first premolar, although it essentially corresponds 

 with the second premolar of the typical dental formula of the 

 Ungulata. In the Camel and Dromedary the actual first premolar 

 is functionally developed and assumes the form of a small canine 

 implanted by a single fang a little way behind the true canine ; it 

 is transitorily represented in the foetus of the true Ruminants ; and 

 is retained only a little longer time in the Llama and Vicugna. (I) 

 The second premolar soon disappears in all the Camelidce ; it is 

 long retained in the true Ruminants, where, as above stated, it 

 is described as the first premolar. The third premolar in the 

 CamelidcB, marked ^ 2 in fig. 2, PL 123, as being that to which 

 the second premolar in the true Ruminants answers, is relatively 

 smaller than that analogue, and is earlier lost, especially in the 

 lower jaw. The last premolar is persistent in the Camelidce, but 

 is smaller and more simple, especially in the lower jaw, than it 

 is in the true Ruminants. The true molars in the Camel are 

 larger in proportion to the size of the head than they are in the 



(1) Cuvier believed the laniariform premolar of the Camel to be the analogue of the first 

 permanent premolar in the true Ruminants, but altered in shape and position. See ' Ossemens 

 Fossiles,' 4to. 1823, torn. Ill, p. 5. The normal number, viz. four premolars and three true 

 molars, was functionally developed in an extinct species of the Deer-tribe, called by Dr. Kaup 

 Dorcatherium, See 'Ossemens Fossiles de Darmstadt', 4to. p. 91. 



