HYRACOIDEA. 565 



Older 6. HYRACOIDEA.* 



Rodent-like plantigrade creatures of small size, with tetradactyl 

 manus and tridactyl pes, short ears and reduced tail. The grinders 

 are rhinocerotine, and there is a centrale in the carpus. 



The affinities of this order are difficult to understand. They 

 have been associated with the Rodentia and with the Ungulata. 

 They are certainly not rodents, and except in the back-teeth it 

 is difficult to see any ungulate features. We have therefore, 

 following Huxley, given them the rank of an order. 



They have close set fur, small ears, and a split snout. The 

 digits have nails, except digit No. 2 of the pes which has a curved 

 claw. 



The dentition is i I, c I, p |, m ;*. The upper incisors have 

 persistent pulps, enamel on the anterior side 'only and are 

 curved as in rodents ; they differ from the corresponding teeth 

 of rodents in being pointed. The lower incisors have den- 

 ticulated crowns and bite behind the upper. There is a diastema 

 and the grinders are lophodont and like those of the rhinoceros. 

 The milk dentition is i il, c }-, m ^, the upper incisors being 

 rooted. 



The jugal extends forwards to the lacrymal and takes part in 

 forming the glenoid cavity which is -transversely placed. The 

 postorbital process of the skull (mainly from the parietal) is con- 

 siderable and nearly meets the jugal. There is an alisphenoid 

 canal. The premaxillae are large. In the vertebral column there 

 are from 28 to 30 dorso-lumbar vertebrae, of which twenty-one 

 or twenty-two are dorsal. There are no clavicles, and the spine 

 of the scapula is without an acromion. The ulna and fibula are 

 complete, and there is a vestige of the pollex. The carpus 

 (Fig. 290) has a centrale and the bones of the two.rows do not 

 alternate. The femur has a small third trochanter. In the pes 

 (Fig. 290) digits 1 and 2 are entirely absent, and the ungual 

 phalanx of digit 2 is cleft. The astragalus presents a shelf on 



* J. F. Brandt, Unters. iib. d. Gattung Hyiax, Mem. Ac. imp. Sci. 

 Petershonrg, 18fi9, (6), 14. O. Thornas, On the species of Hyracoidea, 

 Proc. Zool. Soc. 1892, p. 50. M. Woodward, On the milk dentition of 

 Procavia, rroc. Zool. Soc. 1892, p. 38. George, Ann. Sci. Nat.,(Q), 1, 

 1874. Ameghino,Mammiferes Cretaces de I'Argentine, Bol. Inst. Ge.ogr. 

 Arg., 18, 1897. Fischer, Ban n. Entw. des Carpus u. Tarsus vom Hyrax, 

 Jen. Zeitfichr., 37, 1903, p. 091. 



