VERTEBRATA : MAMMALIA. 727 



size (fig. 415, c) and are placed in the interval between the in- 

 cisors and praemolars. In the upper jaw only the sockets for 

 the canines are left. There are four upper and six lower 

 incisors, which are separated by a wide diastema from the 

 praemolars. The dental formula is 



. 2 2 o o 4 4 3 3 



z - - ; c ; pm : m - - = 38. 



3-3' i i' 33' 3-3 



There is no third trochanter to the femur, but the structure 

 of the manus and pes is quite unknown. 



The only known genera are Toxodon and Nesodon. 



CHAPTER LXXIV. 



HYRACOIDEA AND PROBOSCIDEA. 



ORDER X. HYRACOIDEA. This is a very small order which 

 has been constituted by Huxley for the reception of two or 

 three little animals, which make up the single genus Hyrax. 

 These have been usually placed in the immediate neighbour- 

 hood of the Rhinoceros, to which they have some decided 

 affinities, and they are still retained by Owen in the section of 

 the Perissodactyle Ungulates. 



The order is distinguished by the following characters : 

 There are no canine teeth, and the incisors of the upper jaw are 

 long and curved, and grow from permanent pulps, as they do in 

 the Rodents (such as the Beaver, Rat, &c.) The lower incisors 

 are directed forwards. The molar teeth are singularly like those 

 of the Rhinoceros. According to Huxley, the dental formula of 

 the aged animal is 



**?; ,-; ^4=4 m 3~3 = 6> 

 22' oo 44' 33 



The fore-feet are tetradactylous, the hind-feet tridactylous, and all 

 the toes have rounded hoof-like nails, with the exception of the 

 inner toes of the hind-feet, which have an obliquely-curved nail. 

 There are no clavicles. The nose and ears are short, and the 

 tail is represented by a mere tubercle. The placenta is deciduate 

 and zonary, whereas in the Ungulates it is non-deciduate. 



Several species of Hyrax are known, but they resemble one 

 another in all essential particulars, and, with the exception of 



