320 



MAMMALIA. 



10 <> (8) T . 1 'I 4-4 3-S~l 



Hyrax. Dentition: Q ( . ^ ' \i. ., ., a. ( - p. in. -^ in. I. //. eapensii 



Schreb., Daman, D.issy. liuek-rabliit : Jf. x//ritn-it.t Sdircb. (Fig. (! ( J5) ; probably 

 the (.'oney (Saphan) of the Old Testament. 



\VitJi fi'i- 



Order S. RODEXTIA = GLIRES. 



, clawed <H</ifs. Dentition with 



1(2) 

 1 



chisel- 



incisors, grinding feet,//, witJt transverse enamel folds, and 

 ti'ithunt canines. 



The Rodentia are a large group of small, active Mammalia. They 

 ;ire easily recognizable by the dentition and structure of the teeth. 



The order, nevertheless, 

 includes many forms 

 transitional to the Insec- 

 firora. Rodents are plan- 

 tigrade animals, with 

 freely movable digits. 

 which are usually armed 

 with claws, only rarely 



arched nails? Qr eyen 



hoof -like nails. They all feed on vegetable, usually hard substances,. 

 especially on stalks, roots, seeds, and fruits. Only a few are 

 omnivorous. 



There are two large chisel-shaped, 

 somewhat curved incisors (tig. 696), 

 which possess enamel only on their 

 anterior surfaces. The posterior 

 surface is, therefore, quickly worn 

 away by use, and the more so since 

 the arrangement of the narrow, 

 laterally compressed glenoid cavity 

 necessitates an antero-posterior 

 movement of the lower jaw during mastication. The wearing away is 

 compensated by a proportionate, continous growth of the tooth. The 

 "Tinders, which are separated from the incisors by a wide gap, possess 

 usually transversely arranged folds of enamel, and are only tubercula- 

 ted when the animal is omnivorous. When these teeth are being used 

 the lower jaw is drawn so far back that the incisors are not rubbed 

 one another, and the lower jaw is moved backwards and 



FIG. 696. Skull of Cncettts rnt;/(iris (after 

 Giebel ; Broim's Classen und Ordnuug- 

 en). 



