Sauropsida: Class Reptilia 



475 



Fig. 367. Longitudinal section of nasal region of alligator, (c) Concha; (ms) 

 maxillary sinus; (n) naris; (p) pseudoconcha. (After Gegenbaur. Courtesy, Kingsley : 

 "Comparative Anatomy of Vertebrates," Philadelphia, The Blakiston Company.) 



In reptiles the sense of taste is confined to the mouth. Lack of 

 external organs of taste is probably offset by better development of the 

 nasal organ of chemical sense, the olfactory organ. The efficiency of 

 this organ depends in part on the extent of the nasal surface occupied 

 by the olfactory sensory cells. This surface is increased by various 

 complications of the walls of the nasal cavities. In reptiles the lateral 

 wall of each cavity gives rise to an elongated, inwardly projecting 

 ridge or "shelf," the concha, which is more or less curled downward 

 (Fig. 367). In birds and mammals such conchae are more numerous 

 and more elaborately curled (Figs. 505, 507). The skeletal support of a 

 concha consists of a thin layer of cartilage or bone belonging to the 

 ethmoid region of the cranium. In mammals the keenness of the 

 sense of smell is, in general, correlated with the number and expanse 

 of the conchae. In some amphibians the lateral wall of the nasal cavity 

 bears a low ridge which may be regarded as a weakly developed concha. 

 As to expansion of olfactory surface, therefore, the reptiles are inter- 

 mediate between amphibians and mammals. 



Some reptiles possess what appears to be an accessory olfactory 

 organ, the vomeronasal organ or organ of Jacobson (Fig. 368). 

 It develops as a ventral hollow outgrowth from each nasal cavity, 

 forming a pair of small pouches lying in the anterior region of the 

 roof of the mouth and each opening into the oral cavity by a narrow 

 nasopalatine duct. The two ducts open close together just behind 

 the front teeth and anterior to the internal nares. Nerve-fibers from 

 the olfactory (first cranial) nerve, and some trigeminal (V) fibers, are 

 distributed to the epithelial lining of the organ. The structure and 

 connections of the organ indicate that it may enable the animal to 

 smell substances contained in the oral cavity. Jacobson's organ is 

 well developed in Sphenodon and in lizards and snakes, but absent or 

 rudimentary in crocodilians and turtles. A similar organ occurs in 

 most amphibians but is less well developed than in reptiles. 



Reptilian eyes give evidence of being more effective visual organs 



