516 PHYSIOLOGY CHAP. 



" Stefani described the effects of destroying both lobes of the 

 pigeon as follows : " After recovery from the destruction of the 

 optic lobes, they only show disturbance of vision, relative not absolute 

 blindness, perfectly comparable to that which follows the removal 

 of the cerebral hemispheres in these animals. The pigeon does 

 not fly away when I stretch out my hand to take it up, nor does 

 it peck at the corn in front of it though hungry; but it is able 

 to fly and to avoid obstacles, drops down, perches on objects, or 

 flies to the ground like the healthy pigeons; while the pigeons 

 blinded by removing their eyes remain motionless, and when forced 

 to move only blunder against obstacles." 



The experiments of Jappelli and Sgobbo (1900), who destroyed 

 the corpora quadrigemina in dogs by the ingenious method of 

 introducing a small galvano-cautery like a flexible sound, ending 

 in a tiny platinum loop, into the space between the dura mater 

 and the cerebellum, are specially important. With this instrument 

 they succeeded in obtaining a clean and sharply defined, more or 

 less complete removal of one or other quadrigeminal body on one 

 side, which was aseptic and spared the other tissues. They kept 

 the animals alive till the resulting symptoms were fixed and 

 permanent, and correlated these permanent symptoms with the 

 degree and locality of the lesion. In this way they formed very 

 definite conclusions as to the functions of the corpora quadri- 

 gemina, which partially confirmed those of the earlier observers, 

 partially corrected them, and added new results that harmonised 

 well with the most recent morphological investigations. "We may 

 sum up the conclusions of this important work, keeping as closely 

 as possible to the terms in which they were formulated by 

 Sgobbo : 



(a) Visual disturbance in the eye of the opposite side results, 

 not only from lesions of the anterior quadrigeminal body, as many 

 authors suppose, but also from injury to the posterior body, as 

 had been previously noted only by Lussana and Lemoigne and 

 Bechterew. 



(5) This disturbance consists, not in blindness, but in diminu- 

 tion of vision (amblyopia) in the whole visual field of the eye 

 on the opposite side. This agrees with the observations of Serres, 

 Renzi, and Stefani. 



(c) Lesions of the posterior quadrigeminal body also produce 

 auditory disturbances (deafness and dullness of hearing) in the 

 ear of the opposite side, associated with paresis of the external ear 

 muscles. This observation is new, not having been made by any 

 previous authors. It agrees with the effects of electrical stimula- 

 tion of the posterior quadrigeminal body, which, as we see, causes 

 movements of the ear on the opposite side, and cries. 



(d) The corpora quadrigemina do not contain centres for the 

 movements of the eyeball as other authorities supposed. After 



