ORGAN OF SMELL. 155 



outer wall of the nasal cavity ; and a very small fold, o, close 

 upon the nostril. 



On the surface of these parts is extended a delicate vascular 

 membrane, bedewed with a mucous fluid. The nasal cavities 

 are separated by a septum, which is covered with the same 

 membrane. The prominences, m n o, are attached to the outer 

 wall, not to the septum. Although the analogous parts in the 

 mammalia are supported by osseous plates, named turbinated 

 bones, these prominences being always membranous or cartila- 

 ginous in birds, ought to be named turbinated bodies, rather 

 than bones. The olfactory nerve comes off from the anterior 

 prominence of the cerebrum, at p, proceeds directly forwards 

 in a bony tube, and entering the cavity of the nose at m, is 

 distributed upon the upper turbinated body, and the septum 

 of the nostrils. The passage from the posterior nares to the 

 anterior is subservient to respiration. Its upper part, from m 

 to 0, being formed as in the mammalia, in which observation 

 and experiment have shewn it to be the seat of smell, must be 

 subservient to the same purpose. But although the parts are 

 thus obviously adapted for the perception of odours, it does not 

 appear that birds possess that faculty in a very remarkable 

 degree. It is indeed doubtful whether it be of any use to them 

 in discovering their food. 



No bird is destitute of eyes, or furnished only with imper- 

 fect organs of sight ; but there are birds in which the nostrils 

 are wanting, as I have ascertained by careful dissection. Such 

 are the Gannets and Cormorants. 



Besides the olfactory nerve, there is seen passing across the 

 nasal cavity, a nerve, e m Jc, much larger than the olfactory. It 

 is a branch of the fifth pair, which coming off from that nerve 

 presently after it emerges from the brain, passes obliquely up- 

 wards and forwards, crosses externally the olfactory nerve at 

 its entrance into the nasal cavity, then descends, crosses that 

 cavity, and entering amidst the cellules of the upper jaw, 

 divides into numerous filaments, which are distributed chiefly 

 to the roof of the mouth. It is probably subservient to the 

 sense of taste. 



