The Senses. 313 



with the lateral ventricles. From the olfactory lobes is 

 given off the olfactory nerves, which pass out through the 

 cribriform plate of the ethmoid bone, and ramify over the 

 middle meatus and superior turbinated bone. Owing to 

 the fact that the olfactory nerve is not distributed over the 

 entire area of the nasal chambers, it is usual to divide this 

 cavity into two areas — an olfactory and a respiratory portion. 

 The special nerves of smell ramify in the mucous membrane 

 covering the parts named, but they have no special end 

 organs. In appearance the olfactory, owing to the greyness 

 of its fibres, resembles the sympathetic nervous system. 



In all animals in which the sense of smell is acute the 

 turbinated bones are remarkably convoluted ; this is more 

 marked in carnivora than in herbivora. There are certain 

 substances which excite the olfactory organs more readily 

 than others : thus, in carnivora, flesh, blood, or any animal 

 matter, has a remarkably stimulating effect ; in herbivora, 

 plants, grasses, and vegetable products have a characteristic 

 effect, while the odour of blood is evidently repulsive, and 

 often causes nervousness and fright. Some of the herbivora 

 have remarkably keen scent ; antelopes and deer have the 

 power of smelling the presence of man when even a con- 

 siderable distance away. The sense of smell plays an 

 important part in the sexual relations of animals, for the 

 female in the 'rutting' period may be distinguished at a 

 considerable distance. 



The organ of Jacobson, which is well marked in her- 

 bivora, is said to have some connection with the sense of 

 smell. Cuvier regarded it as the means by which the 

 herbivora distinguished between poisonous and non- 

 poisonous plants. This can hardly be correct; cattle 

 poisoning is comparatively common. 



Before a substance can be perceived by the olfactory 

 nerves, it has to become dissolved in the mucous coating of 

 the part— in fact, it is considered that substances can only 

 be perceived by the sense of smell either in the form of a 

 vapour or liquid, as the sense is nearly or entirely lost if 

 the membrane be dry. 



