THE OLFACTORY NERVES. 515 



rabbit, formed by one of the so-called olfactory nerve roots, which turns 

 inward and crosses the median line, in company with the fibres of the 

 anterior cerebral commissure. 



Physiological Properties of the Olfactory Nerve. The olfactory 

 nerve thus formed is a tract of communication between the central 

 parts of the brain and the olfactory bulb. Its physiological connection 

 with the sense of smell is indicated by, 1st, its anatomical relations ; 

 2d, its comparative development in different species of animals ; and 3d, 

 the results of its injury or disease. 



I. The only anatomical connection of the olfactory nerve, at its 

 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 the parts are highly endowed with the sense of smell. 



II. In such of the lower animals as possess a more acute sense of 

 smell than man, like the dog, the cat, the sheep, and other quadrupeds, 

 the olfactory bulbs are increased in proportion, forming prominent 

 masses at the anterior extremity of the hemispheres ; while the parts 

 representing the olfactory nerves are of so large a size that they are 

 generally designated by the name of the u olfactory lobes." They also 

 contain a central tubular cavity, which is a prolongation from that of 

 the lateral ventricles. There is accordingly a direct correspondence 

 between their development and that of the special sense with which 

 they are connected. 



III. A considerable number of cases are quoted by Longet in which 

 congenital absence of the olfactory nerves, in man, was accompanied by 

 congenital incapacity to distinguish odors ; and others in which a loss 

 of the sense of smell was also observed after morbid affections causing 

 compression or destruction of these nerves. 



According to the experiments of Magendie upon dogs, 1 the olfactory 

 nerves are not sensitive to mechanical irritation, since their compres- 

 sion, puncture, or laceration in various directions, in the living animal, 

 causes no perceptible indications of sensibility. 



Finally, experimental division or destruction of these nerves in dogs 

 abolishes, so far as observation can show, the power of discriminating 

 odors ; although it leaves the nasal mucous membrane sensitive to the 

 irritation of pungent or caustic vapors. In the experiments of Magendie, 

 a dog, after destruction of both olfactory nerves, would disentangle a 

 package containing meat when openly presented to him; but he did 

 not find it, when placed near by without his knowledge. The same 

 result was obtained by Vulpian' 2 in operating upon hunting dogs. 

 These animals, after recovering from the immediate effects of the 

 operation, were kept fasting from 36 to 48 hours, and then introduced 





Journal de Physiologic Experimental^ et Pathologique. Paris, 1825, tome 

 iv. p. 170. 



2 Legons sur la Physiologic du Systeme Nerveux. Paris, 1866, p. 882. 



