NERVOUS SYSTEM. 



tomical connection of the optic thalami with the sensory 

 tracts, though, in experiments on animals, destruction of 

 these parts does not necessarily affect the general sensibility. 



Tubereula Quadrigemina. 



These little bodies, sometimes called the optic lobes, are 

 rounded eminences, two upon, either side, situated just be- 

 hind the third ventricle. The anterior, called the nates, 

 are the larger. These are oblong and of a grayish color ex- 

 ternally. The posterior, called the testes, are situated just 

 behind the anterior. They are rounded, and rather lighter 

 in color than the anterior. Both contain gray nervous mat- 

 ter in their interior. They are the main points of origin 

 of the optic nerves, and are connected by commissural fibres 

 with the optic thalami. In birds, the tubercles are two in 

 number, instead of four, and are called the tubercula bi- 

 gemina. 



It is probable that the tubercula quadrigemina are in ex- 

 citable and insensible. "When pain and convulsive move- 

 ments have apparently followed their mechanical irritation 

 in living animals, these phenomena have probably been due 

 to excitation or stimulation of the motor or sensory commis- 

 sural fibres which pass beneath them. At least, this seems 

 to be the proper conclusion to draw from the experiments 

 of Longet. 1 



As regards the function of the optic lobes, aside from 

 their action as reflex nervous centres for the movements of 

 the iris, there is little to be said, except that they preside over 

 the sense of sight. They are easily reached and operated 

 upon in birds, where they are very large, and, as Flourens 

 demonstrated many years ago, their extirpation is followed 

 by total loss of sight, as well as abolition of the reflex move- 

 ments of the iris. 8 In birds and in those mammals in which 



1 LONGET, Traite de physiologic, Paris, 1869, tome iii., p. 407. 

 8 FLOURENS, Sysieme nerveux, Paris, 1842, p. 145. 



