320 



MAMMALIA. 



H. 



Hyraz. Dentition : \ | [i. .. <j ,. . g M. f|) 



Schreb., Daman, Dassy, Kock-rabbit ; H. syriacus Schreb. (Fig. 695) ; probably 

 the Coney (Saphan) of the Old Testament. . 



Order 8. RODENTIA = GLIRES. 



With freely movable, clawed digits. Dentition with 



1(2) 

 1 



chisel- 



shaped incisors, grinding teeth with transverse enamel folds, and 

 without canines. 



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

 are easily recognizable by the dentition and structure of the teeth. 



The order, nevertheless, 

 includes many forms 

 transitional to the Insec- 

 tivora. Rodents are plan 

 tigrade animals, with 

 freely movable digits, 

 which are usually armed 

 with claws, only rarely 

 with arched nails, or even 

 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 (fig. 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, coiitinous growth of the tooth. The 

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

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

 tecl 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 

 against one another, and the lower jaw is moved backwards and 



FIG. 696. Skull of Cricetus vulgaris (after 

 Giebel ; Bronn's Classen und Ordnung- 

 en). 



