422 THE NEEVOUS SYSTEM. 



descending degenerations take place without any accompanying lesion 

 of the cerebral ganglia, and they are not produced by similar morbid 

 alterations of the cortex in other parts of the brain. Instances of this 

 kind, observed during a period of fifteen years, point to an immediate 

 connection of certain fibres of the crus cerebri and internal capsule with 

 the central convolutions of the cerebral hemispheres. 



2d. The direct occipital fibres of the crus cerebri constitute a distinct 

 tract on its external border, which turns outward beneath the extremity 

 of the optic thalamus, and, forming the posterior part of the internal 

 capsule, curves backward toward the occipital convolutions. This 

 tract, which was described by Gratiolet,* from the dissection of brains 

 hardened in alcohol, has been recognized by Meynert and Huguenin, 

 and is generally admitted on anatomical grounds. Its existence, as 

 well as the sensitive character of its fibres, is furthermore indicated by 

 the fact that destructive injuries of the posterior part of the internal 

 capsule, in which it is situated, produce loss of sensibility on the oppo- 

 site side of the body. 



Physiological Properties and Function of the Hemispheres. The 

 most important function belonging to the hemispheres, as a whole, is no 

 doubt connected with the exercise of the intelligence. It is this part 

 of the brain which is most developed in man as compared with the 

 lower animals ; and of all the nervous endowments it is the intellectual 

 faculties in which he is most distinctly their superior. There are 

 furthermore a number of special considerations which show that the 

 cerebral hemispheres are in some way the especial organ of the mind. 



I. It is certain in the first place that the hemispheres are not directly 

 connected with the maintenance of physical life, and are not, even in 

 man, essential to its continuance. They may be completely removed, 

 on both sides, in fishes, reptiles, birds, and even in some mammalians, 

 as the rabbit and the rat; and in the higher quadrupeds large portions 

 of their substance may be destroyed, leaving all the vital functions in 

 continued activity. In man they may suffer extensive morbid altera- 

 tions or mechanical injurie^, accompanied by loss of substance, without 

 fatal result. One of the most marked instances of this kind is that 

 reported by Bigelow,f in which a pointed iron bar, over one inch in 

 thickness, was driven through a man's head by the premature blasting 

 of a rock. The bar entered the left side of the face near the angle of 

 the jaw, and passed obliquely upward, inside the zygomatic arch and 

 through the anterior part of the cranial cavity, emerging from the 

 frontal bone at the median line, just in front of the union of the coro- 

 nal and sagittal sutures. The patient became delirious within two 

 days after the accident, remaining partly delirious and partly comatose 

 for about three weeks. He then began to improve, and at the end of 

 rather more than two months from the date of the injury was able to 



* Anatomie Cornparee du Syste'me Nerveux. Paris, 1857, p. 186. 



f American Journal of the Medical Sciences. Philadelphia, July, 1850. 



