HYRACOIDEA. 705 



One or two median horns grow as huge warts from the snout 

 and forehead. The dentition is very variable, but the back 



teeth — are almost uniform ; there are no upper canines, but 



4, 3 

 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 — 

 Lophiodontidfe (Eocene), e.g. Lophiodon, Hyracotherium, 

 Systemodon, — a family perhaps ancestral to most of the 

 modern Perissodactyla. 

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

 Anchitherium. 

 Other remarkable types — 



Lambdotherium , Chalicotherium, Titanotherium, 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 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 |^, the permanent is ^ 3 . 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 cseca 



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