xiv. g 



RECEPTOR ORGANS 



385 



tory behaviour in exposing itself to sunlight. It is also possible that the 

 pineal complex plays some part in the control of reproduction. 



In the majority of reptiles the olfactory region of the nose is quite 

 well developed, but, except in crocodiles, there is only a single nasal 

 concha. The organ of Jacobson (vomero-nasal organ), a specialized 

 and sometimes separate region of the nose, innervated by a separate 



THIS SIDE, 

 RELAXATION 



THIS SIDE, 

 ACCOMMODATION 



Fig. 218. Diagram to show the mechanism of accommodation in the eye of 



reptiles. 



ap. annular pad of lens; bm. Brucke's muscle; bp. base plate of ciliary body; c. cornea; ch. 

 chorioid; cp. ciliary process; 1. iris; lb. lens body; ot. ora terminalis; pi. pectinate ligament; 

 s.s. sclera; sc. scleral cartilage; scs. sclerocorneal sulcus; so. scleral ossicle; sr. sensory retina; 

 tbm. tendon of Brucke's muscle (continuous with inner layers of corneal substantia propria); 

 //. tenacular ligament; z. zonule. (From Walls, The Vertebrate Eye.) 



branch of the olfactory nerve, is present in turtles, Sphenodon, and 

 Squamata. In the latter it is usually very highly developed (see 

 p. 405). 



The tympanum when present lies at the back of the jaws, sunk a 

 little below the surface. The range of response to sound waves is not 

 known in lizards, but the ears of certain tortoises are very sensitive 

 to sound over a narrow range of about no cycles per second; appar- 

 ently there is some resonating mechanism, perhaps the columella auris, 

 which vibrates at this frequency. Generally speaking, the sense of 

 hearing is best developed among reptiles in the Crocodilia and certain 

 lizards. 



