448 THE NERVOUS SYSTEM. 



nerve supplies only the muscles of the tongue, its associate, the glosso- 

 pharyngeal, sends part of its sensitive fibres to the tongue and part 

 to the pharynx ; and while the trigeminal nerve is mainly distributed 

 to the external parts of the face, one of its deeper branches, the lingual, 

 is distributed to the tongue. The arrangement, however, is substan- 

 tially correct, and may serve as a useful guide in the study of the 

 nervous functions. 



First Pair. The Olfactory Nerves. 



What is called in man the " olfactory nerve," is a prismatic extension 

 of gray and white substance, running in a longitudinal groove on the 

 under surface of the anterior cerebral lobe, near the median line, and 

 terminating anteriorly in a flattened ovoid mass of gray substance, the 

 "olfactory bulb." The olfactory bulb rests upon the cribriform plate 

 of the ethmoid bone, and gives off, through the perforations in this 

 bone, the nervous filaments supplying the olfactory membrane in the 

 nasal passages. The prismatic mass connecting the olfactory bulb with 

 the rest of the brain is, in reality, an extension of the anterior lobe, and 

 forms part of the cerebral convolutions. In most quadrupeds it is 

 much larger than in man, often enclosing a prolongation of the lateral 

 ventricle; and in size and structure it exhibits so close a resemblance 

 with the remaining convoluted portion of the brain, that it is properly 

 designated as the " olfactory lobe." In man it is so slightly developed 

 that this term can hardly be applied to it ; but it nevertheless consists 

 partly of gray substance, and shows only on its superficial border a 

 longitudinal striation of white substance, which connects the olfactory 

 bulb in front with the central parts of the brain behind. 



The olfactory apparatus consists accordingly of, 1st, the olfactory 

 nerves proper, distributed upon the mucous membrane of the upper 

 part of the nasal passages, and connected at their central extrem- 

 ity with the gray substance of the olfactory bulb ; 2d, the olfactory 

 bulbs, situated on the anterior extremity of the olfactory lobes, and 

 giving origin, as above described, to the nerves of the olfactory mem- 

 brane ; and 3d, the olfactory tracts, that is the longitudinal bands 

 of white substance, running along the superficial border of the olfac- 

 tory lobes (commonly called " olfactory nerves "), toward the central 

 parts at the base of the brain. 



Physiological Properties of the Olfactory Nerve. The connection 

 of the olfactory nerve with the sense of smell is indicated by, 1st, its 

 anatomical relations ; 2d, its comparative development in different ani- 

 mals ; and 3d, the results of its injury or disease. 



I. The only anatomical connection of the olfactory tracts, at their 

 anterior extremity, is with the olfactory bulb ; and the nerve fibres 

 given off from this part are distributed only to the olfactory region 

 of the nasal passages. In this region ordinary sensibility is but 

 slightly developed, while it is highly endowed with the sense of smell. 



II. In animals possessing a more acute sense of smell than man, like 



