684 THE CEREBRUM 



fibers form a longitudinal bundle which is designated as the median 

 fillet or lemniscus. They terminate chiefly in the thalamus superior 

 colliculus of the corpora quadrigemina, receiving in their course nu- 

 merous fibers from the sensory nuclei of the cranial nerves of the oppo- 

 site side. The thalamus is connected by tertiary neurons with the 

 parietal region of the cerebrum. This explains the observation of 

 Campbell, 1 that the degenerative changes associated with tabes dor- 

 salis, finally progress into these central paths and also affect the cells 

 of the post-Rolandic region. 



Regarding the character of the sensations mediated by this area, 

 it has been stated by Luciani and Seppilli that they subserve the 

 muscle and cutaneous senses. But as pain is not felt as a result of 

 the stimulation of this area, it may be said that it is chiefly concerned 

 with muscular and tactile sensibility, and in a lesser degree also with 

 the temperature sense. The fact that the perceptions and judgments 

 based upon these sensations are mediated in the association realm of 

 this region, is especially well betrayed by the diminution and loss of 

 the stereoscopic acuity (astereognosis) invariably following lesions of 

 this area. In other words, defects of the post-Rolandic region give 

 rise to a more or less imperfect judgment of the shape and texture .of 

 objects when handled. Doubtlessly, therefore, this psychical difficulty 

 must be dependent upon a loss of those associations which are ordina- 

 rily obtained with the help of the cellular units of this area. Another 

 psychic defect frequently associated with injuries to this region, is 

 tactile agnosia, i.e., an inability to form judgments regarding the 

 ordinary sensations of touch. 



THE PSYCHO -VISUAL REGION 



The Visual Center. The fact that vision is under the control of 

 a definite region of the cerebral cortex was discovered by Panizza in 

 1855. It was found that an injury to one posterior tip of the cerebrum 

 of the dog gives rise to blindness in the opposite eye. This same obser- 

 vation was made subsequently by Hitzig (1874), but without knowing 

 that it had already been called attention to previously. It was left 

 to Munk (1878) to prove that the destruction of certain parts of the 

 occipital lobes leads to total psychical or cortical blindness. These 

 terms were used to indicate that the loss of vision is not due in this 

 particular case to a functional uselessness of the retina or of the re- 

 fracting media of the eyes, but to a central defect involving the 

 perceptions and judgments pertaining to visual sensations. Omitting 

 the controversial discussions arising in consequence of this discovery 

 which were participated in by Goltz and Luciani, it may be stated 

 in brief that the more recent experiments have fully substantiated 

 these results of Munk. 2 Thus, Schaeffer (1888), Brown (1890), and 



1 Histol. Studies on Localization of Cerebral Functions, Cambridge, 1905. 



2 tJber die Funkt. der Grosshirnrinde, Berlin, 1890, and Berliner Akad. der 

 Wissenschaften, 1892-1901. 



