240 



ELEMENT A RY ANA TOM Y. 



[LESS. 



or be so placed as to resist the friction produced by sitting on 

 rough branches, as in the commoner Monkeys of Africa and 

 India. 



A familiar and very valuable modification of the epidermic 

 skeleton is known to us under the name of " tortoise-shell, 1 



FIG. 204. VENTRAL SURFACE OF THE PLASTRON OF A FRESH-WATEK 

 TORTOISE (mys). 



The bony scutes are nine in number, ic, inter-clavicular scute ; c, clavicular 

 scute ; hy, hyo-sternal scute ; ftp- hypo-sternal scute ; xp, xiphi-sternal scute. 



The horny epidermal scales are twelve in number, as indicated by the dark lines ; 

 one such traverses each xiphi-sternal and hypo-sternal near its middle. 



which coats externally the rigid and solid bony armour of a 

 certain kind of Turtle. An essentially similar though com- 

 mercially valueless structure also invests the armour of almost 

 all kinds of Tortoises and Turtles, and consists of plates 

 disposed in regular series upon the back and on the belly. 



8. The true DERMIS often becomes ossified, constituting an 

 exo-skeleton of the most unequivocal kind. 



An example of such a condition is 

 to be found even in man's own class, 

 Mammalia, namely, in the Arma- 

 dillos. These creatures possess a very 

 complete armour, formed of small, 

 many-sided, bony plates (termed 

 scutes), with their margins adjusted 

 together, aggregated in masses differently in different kinds. 

 There is generally one mass, or shield, on the head, one 

 on the shoulders, one on the loins, with narrow bands of 



FIG. 205. ARMADILLO. 



