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REPTILES 



the apertures in front and behind. In certain instances, as in 

 the box-tortoises, more effectual protection is afforded by the 

 development of transverse hinges in the plastron, which is thus 

 provided with movable flaps, completely closing the two aper- 



Fig. g. — A, lateral, B, dorsal views of the skull of a Horned Dinosaur (Tri- 

 ceratops fiabellatus) showing horn-cores and neck-shield, a, nostrils; b, orbit; 

 c, supratemporal vacuity; e, small bones round occiput; //, left horn-core; h', 

 horn-core on nose ; p, predentary bone; q, quadrate bone; r, rostral bone. 



tures when the animal is withdrawn into its shell. On the other 

 hand, in the marine turtles, which do not require such complete 

 protection, the upper and lower halves of the shell are discon- 

 nected, and the head and neck cannot be drawn within the mar- 

 gins of the carapace. As mentioned in an earlier paragraph, the 



