HYRACO1DEA. 763 



sometimes a large lower pair ; there are a few incisors, but these 

 are often small and deciduous. 



There are several entirely extinct families of Perissodactyla, such as 

 Lophiodontidse (Eocene), e.g. Lophiodon^ Hyracotherium, Sys- 



temodon, a family perhaps ancestral to most of the modern 



Perissodactyla. 

 Palseotheriidse (Eocene to Miocene), e.g. Palaotherium and 



Anchitherium. 



Other remarkable types Lambdotherium^ Chalicotherium, Titano- 

 therium t of elephantine size, and the specialised Macrauchenia 

 are referred to distinct families. 



Sub-Order HYRACOIDEA 



An isolated order of small Rodent-like Ungulates, repre- 

 sented by Hyrax (Procavia) and Dendrohyrax, living in 

 rocky regions and on trees in Africa and Syria. The 

 species (14) are adept climbers. 



The upper incisors have persistent pulps, and are curved 

 as in Rodents, but they are sharply pointed, not chisel- 

 edged. The outer lower incisors are straight, and have 

 trilobed crowns. There are no canines in the second set, 

 but the upper milk canine sometimes persists; and there 

 is a wide space between incisors and premolars. The back 

 teeth are very uniform, and like those of Perissodactyla. 

 The milk dentition is f^, the permanent is ~^. Hyrax is 

 one of the few Mammals in which the first premolar is a 

 replacing tooth. The jugal forms part of the glenoid cavity 

 (cf. Marsupials). 



In the fore-feet the thumb is rudimentary, the little 

 finger is smaller than the median three, which are almost 

 equal. In the hind-feet, which are like miniatures of 

 those of the rhinoceros, the hallux is absent, and the 

 fifth toe is rudimentary. There are no hoofs in the 

 strict sense. There are no clavicles. The tail is very 

 short. 



The brain is like that of Ungulates. The stomach is 

 divided into two parts by a constriction. In addition to 

 the short but broad caecum, there are two supplemental 

 caeca lower down on the intestine. The testes are 

 abdominal. Of the mammae, four are on the groin and 

 two are axillary. The placenta is zonary, as in the Pro- 

 boscklea and Carnivora. A few extinct forms are known. 



