FUNCTIONS OF THE PONS VAROLII. 283 



medulla oblongata. They accordingly receive, conduct, or transmit 

 the effects of sensory impressions, upwards to the cerebrum ; and, in 

 particular cases, probably also transfer and radiate such impressions. 

 They also conduct the voluntary motorial stimulus, downwards from 

 the cerebrum to the medulla and cord. The paths of sensation are 

 probably through the gray matter and white fibres of the central and 

 posterior portions of the pons and of the cerebral peduncles; whilst 

 the paths of motion are down through the white fibres forming their 

 anterior or under portions. Furthermore, the gray matter of these 

 parts forms reflex centres for the performance of most extensive and 

 powerful reflex acts, being, in this sense, quite as energetic as the 

 medulla oblongata and cord. Some of these reflex movements are of 

 a local kind, such as those which regulate certain of the movements 

 of the pupil ; others are of so general and purposive a character, as to 

 have led to the supposition that here, at length, we arrive at a portion 

 of the nervous centres, in which not only conscious sensation may be 

 realized, as supposed by Longet, but in which some feeble mental di- 

 rective power may be exercised. But this is not proved. 



In animals in which, the cerebrum and cerebellum being taken 

 away, the pons and medulla oblongata are left uninjured, and connected 

 with each other, cries and attempts to remove the objects of irritation, 

 have been found to follow pinching the tail, and the application of am- 

 monia to the nose; if left quiet, the animal remains motionless, but 

 if put into an uncomfortable position it immediately resumes a more 

 easy one. All such movements, however, cease when the pons is re- 

 moved from the medulla. (Flourens, Longet.) The movements appear 

 to be as perfect as the natural sensori-motor reflex movements, and re- 

 semble the instinctive movements of animals, but they are not really 

 voluntary. 



Experiments on the pons and cerebral peduncles are followed by 

 remarkable results. Thus, irritation of the deep parts of the pons 

 causes convulsions in various regions of the body, and, if the brain be 

 left, obvious signs of sensibility. A section of the transverse fibres 

 of the pons leading to the cerebellum on one side causes most curious 

 rotatory movements on the part of the animal, which turns towards the 

 injured side, contrary to what happens in certain other examples of 

 rotation to be presently mentioned, produced by sections of other parts 

 of the nervous centres. Section of the corresponding fibres on the 

 opposite side arrests this rotatory movement. Division of these fibres 

 on one side also produces a downward movement of the -eyeballs on 

 the injured side, and convulsive rolling movements in the eye of the 

 opposite side. Lastly, a hyperaesthesia similar to that which follows 

 sections of the spinal cord, especially of its posterior portion, occurs 

 after sections of the back or front of the pons ; but this is noticed on 

 the opposite side of the body, and not on the same side, as is the case 

 when the cord is injured. 



The cerebral peduncles are, like other portions of the longitudinal 

 parts of the nervous centres, conductors of sensorial, voluntary, and 

 reflex impressions, upwards and downwards, along special sets of 

 fibres, set apart for each function. Thus, the sensorial. paths are 



