264 



COMPARATIVE ANATOMY 



complicated later by the development of blind pouches or grooves, 

 which are, however, more marked in Anura, and more especially 

 in Gymnophiona, than in Urodela. The prominences or ridges 



projecting into the nasal lumen 

 between the pouches are analo- 

 gous to the turbinals of higher 

 forms. A main chamber and a 

 more laterally situated accessory 

 cavity can be distinguished, the 

 latter extending into the maxil- 

 lary bone (Fig. 193). In certain 

 Gymnophiona the accessory cham- 

 ber becomes entirely shut off from 

 the main cavity and receives a 

 special branch of the olfactory 

 nerve, so that in these cases two 

 separate nasal cavities can be 

 distinguished. The external nos- 



FIG. 192. OLFACTORY ORGAN OF Nee- trils are always lateral in the 



adult, but in Urodeles, this 

 position is attained secondarily. 

 A F, antorbital process ; F, frontal ; They are opened and closed by 



N, olfactory sac; Of, olfactory mil o O l P< , 

 nerve ; P, process of the parietal ; 



'Pmz, premaxilla ; PP, palatoptery- Glands, situated under the 



goid. olfactory mucous membrane, are 



now met with in terrestrial forms ; 



these are either diffused, or united to form definite masses. They 

 either open directly into the nasal cavity, their secretion serving 

 for the necessary moistening of the mucous membrane (effected 

 in Fishes and in larval and perennibranchiatc Amphibians by 



turns macnlatus. From the dorsal 

 side. 



FIG. 193. TRANSVERSE SECTION THROUGH THE OLFACTORY CAVITIES OF 

 Plethedon ylutinosus. 



C, cartilaginous, and S l , fibrous portion of the turbinal, which causes the 

 olfactory epithelium (E) to project far into the nasal cavity ; F, frontal ; 

 ID, intermaxillary gland, shut off from the cavity of the mouth by the oral 

 mucous membrane (MS) , K, maxillary cavity ; M, maxilla : N, main nasal 

 cavity ; Pf, prefrontal ; Sp, nasal septum ; 8, S l , olfactory mucous mem- 

 brane ; Vop, vomero-palatine. 



the external medium), or they pour their secretion into the 

 pharynx or posterior nostrils. The latter are always situated 



