178 



COMPARATIVE ANATOMY. 



This definition applies accurately to the accessory nasal cham- 

 ber of Caecilians already mentioned, which is enclosed within 

 the maxillary cavity, and there can be no doubt that the latter 

 is homologous with the maxillary sinus of all Vertebrates. In no 

 other Vertebrates, however, does it retain the character of a kind 

 of separate nasal chamber, but on the contrary, the higher we pass 

 in the Vertebrate series, the more does the maxillary cavity become 



FIG. 148. DISSECTION OF THE HEAD OF Epicrium glutinosum. (Dorsal view.) 

 VH, cerebral hemispheres, separated by a furrow (F) from the olfactory lobes (Lol) J 

 Z, pineal gland ; MH, mid-brain ; HH, cerebellum ; NH, medulla oblongata > 

 R, spinal cord ; Se, septum nasi ; I d , dorsal pair of olfactory nerves ; V a > V b , V c , 

 first, second, and third division of the trigeminal ; V al and F a2 , lateral branches 

 of the first division, one of which goes to the olfactory mucous membrane, and 

 the other to the sheath of the " tentacle " (TtS] : the constrictor muscle of the 

 tentacular gland (Cg) is supplied from a lateral branch of the second division of 

 the trigeminal ; X, vagus ; ca, duct of the tentacular gland, which is surrounded 

 by the sheath of the tentacle ; Boc, globe of the eye ; mass, mass 1 , the two 

 portions of the masseter muscles ; Oh, auditory capsule. 



separated physiologically from the olfactory organ; it loses its 

 olfactory epithelium, and finally degenerates into a simple air- 

 sinus. 



In Lizards and Snakes an apparatus exists which is quite 

 unconnected with the Jacobson's organ of Gymnophiona, but which 

 nevertheless comes under the above definition. This (see Fig. 

 145, P) lies between the floor of the nasal cavity and the roof of 

 the mouth, and rnay be described as a small paired cavity lined by 



