362 



ZOOLOGY 



As an example of the structure of a reptile, we may consider 

 the anatomy of the turtle. 



General form of body. — The turtle is depressed and 

 roimded, and the trunk carries an upper and a lower plate, 

 affording protection to the entire body. 



Skeleton. — The vertebrae are few, in correspondence with 

 the shortened body, and are immoval)le upon each other (Fig. 

 330). The spines of the vertebrae are flattened out to form 



the median row of Ijony 

 plates, and the ribs are 

 flattened to form the 

 " costal " plates. These, 

 with certain plates at 

 the margin, form the 

 " carapace " of the 

 turtle. The bony cara- 

 pace is covered b}' hornj' 

 plates which are derived 

 from the skin, and only 

 roughh' agree with the 

 bony plates lying below 

 them. The breast-bone and ventral ribs are replaced by 

 the " plastron," which is made u]) of four paired and one 

 median jilate. The skull is massive, and the bones of the side 

 of the head form a Ijroad arch, enveloping and protecting, but 

 separated by a sjiace from, the brain-case proper (Fig. 331'). 

 The shoulder and pelvic girdles arc fused with the shell, but 

 the skeleton of th(> appendages is tyjiical, though often show- 

 ing special adaptations for swinnning. 



The organs of nutrition. — Tlie food of turtles is extremely 

 varied, according to their habitats. Land tortoises eat toad- 



Fn:. aSl. — Skull of a turtle (Chclonc) \-ifwed 

 from the left .side. Ttie boncw shown are 

 named from in front backward : Mx, ma.x- 

 illary ; F, frontal ; ./, jugal ; Pt.f, post- 

 frontal ; Qj, quadrato-jugal ; Q, quadrate ; 

 Sg, squamosal ; Pnr, parietal : -S.o, supra- 

 occipital. Fr(tm " C'ambriflge Nat. Hist." 



