I2IO HUMAN ANATOMY. 



The cortex is supplied by pial vessels distinct from those supplying the basal 

 ganglia and adjoining regions. The latter come directly from the branches of the 

 circle of Willis at the base. The cortical vessels anastomose ; those in the region 

 of the basal ganglia do not. The latter are ' ' end arteries, ' ' so that when one is 

 plugged by an embolus the part supplied is deprived of blood and undergoes 

 necrosis (softening of the brain). In such a case the cortical supply would not be 

 permanently interfered with. When a cortical arteriole is blocked, the anastomosis 

 may furnish a sufficient collateral circulation to prevent necrosis in the affected 

 part, but cortical softening is exceedingly common. When one of the arteries forming 

 the circle of Willis is occluded, as an internal carotid by ligation of the common 

 carotid, the anastomosis in the circle is so free that, in most cases, no marked 

 effect is apparent. Cerebral disturbances, as delirium or convulsions, do occur in 

 some cases, and in some are fatal. Even when both carotids are ligated, with an in- 

 terval of some days or weeks, the operation is not more frequently followed by cere- 

 bral disturbances than when only one is tied (Pilz). A case in which the patient 

 lived after one carotid and one vertebral had been obliterated by disease, and the 

 other carotid ligatured, has been reported (Rossi). In another case, although both 

 carotids and both vertebrals had been occluded, the patient lived a considerable time 

 afterward, the cerebral circulation being maintained through the medium of anas- 

 tomosis of the inferior with the superior thyroids, and the deep cervical with the 

 occipital artery (Davy). Occasionally ligation of the carotid has been followed by 

 hemiplegia. 



The most common seat of intracerebral hemorrhage is near the basal ganglia in 

 the region of the internal capsule. The artery most frequently at fault is a branch of 

 the middle cerebral, the lenticulo-striate, or artery of Charcot (page 1207). Hemor- 

 rhages occur with less frequency in other portions of the cerebrum, and much more 

 rarely in the pons, medulla oblongata, and cerebellum. The symptoms produced by 

 the hemorrhage are the result of destruction of tissue and of pressure upon adjacent 

 parts, and will vary according to the seat of the lesion. Tumors or inflammatory 

 products will produce essentially the same symptoms. 



Cerebral Localization. — In order to understand the nature of the symptoms 

 produced by brain lesions it will be necessary to study at least some of the functional 

 areas of the cortex and their paths of conduction through the brain substance. 



Taylor has summarized as follows the researches of His and of Flechsig, which 

 are of comparatively recent date and have thrown new and valuable light upon the 

 functions possessed by the cortical regions of the brain, by the study of their mode of 

 development. Flechsig succeeded in following the various tracts through their 

 myelination. The tracts which are functional earliest receive their myelin before the 

 others. He has shown that the fibres in the spinal cord, medulla, pons and corpora 

 quadrigemina are almost entirely meduUated when the higher parts show little or no 

 myelin. In the new-born child the cerebrum is almost entirely immature, and 

 proportionately few of its fibres are medullated. 



According to Flechsig, the sensory paths in the brain first become medullated, 

 and may be observed developing one after another, beginning with that of smell and 

 ending with that for auditory impulses from the periphery to the cortex. In this 

 way it has been ascertained that the individual sensory paths terminate in tolerably 

 sharply circumscribed cortical regions, for the most part widely removed from one 

 another, being separated by masses of cortical substance which remain for a consid- 

 erable period immature or undeveloped. The cortical sense areas thus mapped out 

 correspond entirely to those regions of the surface of the brain which pathological 

 observation has shown to stand in relation to the different qualities of sensation. 

 Olfactory fibres are found to end mainly in the uncinate gyrus. Visual fibres have 

 been traced to the occipital lobe in the neighborhood of the calcarine fissure, and 

 auditory fibres to the temporal lobe. Flechsig has further obser\^ed that new paths 

 begin to develop from the points where certain of the sense fibres terminate and pur- 

 sue a downward course. They can be followed from the cortex to the medulla and 

 to the motor nuclei of the cord. These descending paths are mainly those known as 

 the Pyramidal or motor tracts, and the area from which they proceed, commonly 

 called the Rolandic region, is, according to Flechsig, concerned also in the sensation 



