DR. KILL, FROM REFLEX ACTION TO VOLITION. 45 



Now we know that it, like the spinal cord, is a network which 

 receives afferent or sensory fibres, and gives origin (from large 

 cells which look after their nutrition) to efferent or motor 

 ones. A vast aggregation of sensory-motor arcs. Recent in- 

 vestigations have further shown that the fibres which reach 

 the cortex do not come promiscuously from all parts of the 

 lower network, but that it is divided into areas, each of which 

 is in connection, through its lower centre in the spinal cord 

 and the rest of the central grey matter, with a particular sense 

 organ. We owe this discovery entirely to experiment, but the 

 information obtained by stimulating or excising particular 

 regions of the brain can be checked by appeal to other 

 classes of evidence. 



Among animals we can easily pick out certain ones whose 

 sensory endowments differ conspicuously from those pos- 

 sessed by most other members of their group. For example, 

 aquatic mammals are deficient hi the sense of smell; whether it 

 be because the mammalian organs of olfaction are only adapted 

 for the recognition of bodies suspended in a gaseous medium 

 and cannot be used for the recognition of substances in 

 solution ; or whether it be that the respiratory apparatus is 

 closed when the animal is under water, and so there is no 

 opportunity for the renewal of the fluid which fills the 

 nostril, it is a notable fact that however far the groups to 

 which particular aquatic animals respectively belong are 

 removed from each other, the sense of smell is in abeyance in 

 every case. Whales, dugongs, seals, &c, resemble one another 

 in having but little sense of smell or none at all. And with 

 the dwindling of the sense of smell is associated deficiency 

 of the region of the brain known as the temporo-sphenoidal 

 lobe. Dogs and other cursorial carnivora on the contrary 

 possess this sense highly developed, and show a correspond- 

 ing development of this region of the brain. The herbivora 

 are remarkable for their acuteness of vision, with which is 

 associated a fulness of the occipital lobe. Cats and other 

 crouching carnivora hunt largely by the sense of hearing. 

 Otters find their way among the snags and roots which over- 

 hang the dark pools in which they seek their prey, with the 

 aid of the sensitive bristles of the cheek. This list might be 

 almost indefinitely multiplied, but we find from the result of 

 observations upon the brains of animals, as well as from the 

 results of experiment and the observations of disease, that 

 the cortex of the brain is mapped out into areas of separate 

 occupation. There is no division into regions allocated to 



