352 IKNERVATION. [CHAP. XI. 



to nerves of sensation, are, in our judgment, sufficient anatomical 

 facts to warrant the opinion that the thalami must perform a func- 

 tion which, although it may be subservient to, or associated with, 

 that of the striated bodies, is yet entirely dissimilar in kind. 



It has been supposed that the corpora striata are special centres 

 or ganglia to the olfactory nerves, and to the sense of smell. But 

 such a supposition is altogether superfluous, inasmuch as a very 

 distinct and obvious centre to these nerves exists in the olfactory 

 process or lobe, miscalled nerve by descriptive anatomists. The 

 small olfactory nerves are implanted in the anterior extremity or 

 bulb of this process, which is provided with all the structural 

 characters of a nervous centre, and contains a ventricle. This 

 lobe, moreover, is always developed in the direct ratio of the size 

 and number of the olfactory nerves, and of the development of 

 the sense of smell; and in the Cetacea, a class in which the 

 olfactory nerves and process either do not exist at all, or are so 

 imperfectly developed as to have escaped the notice of some of the 

 ablest anatomists, the corpora striata are of good size proportionally 

 to that of the entire brain. 



Corpora Quadrigemina. The marked connexion of these gangli- 

 form bodies with the optic nerves plainly indicates that they bear 

 some special relation to those nerves, and to the sense of vision ; 

 and this indication becomes more certain when we learn, from 

 comparative anatomy, that in all vertebrate tribes in which the 

 encephalon is developed, special lobes exist, bearing a similar 

 relation to the optic nerves (pp. 274 5). When the optic 

 nerves are large, these lobes are large ; and in the Pleuronecta, in 

 which the eyes are of unequal size, Gottsche states that the optic 

 lobes are unequal. Still, as Serres has remarked, the quadrigeminal 

 tubercles probably perform some other office besides that which 

 refers to vision ; inasmuch as the absence, or extremely diminutive 

 size, of the optic nerves in some animals (the mole for instance) 

 does not materially affect that of these bodies.* 



Flourens found that destruction of either of these tubercles on 

 one side was followed by loss of sight on the opposite side, and con- 

 sequently that the removal of both deprived the animal altogether of 

 the power of vision, but did not affect its locomotive or intellectual 

 power, nor its sensibility, except to light. In these experiments the 

 action of the iris was not impaired if the tubercles were only par- 

 tially removed ; as long as any portion of the roots of the optic 



Cyclop. Anat., art. Optic nerves. 





