ON SOME HISTOLOGICAL FEATURES OF THE BRAIN. 655 



hence the number of fibrils in it may be spoken of as enormous. These 

 fibrils seem certainly to be connected on the one hand with the cells of the 

 nuclear layer, and on the other hand with the scattered small cells of their 

 own layer ; but we have no evidence that these two sets of fibrils are con- 

 tinuous with each other ; on the contrary, it seems more probable that the 

 two sets of cells represent two independent systems. We can hardly doubt 

 that these fibrils are in functional connection with the medullated fibres of 

 the central white matter ; but we have no clear evidence that the system 

 of scattered cells is continuous either with the cells of Purkinje, and so with 

 the medullated fibres belonging to those cells, or with the medullated fibres 

 which end independently in the molecular layer ; and we have no evidence 

 at all that the system of the cells of the nuclear layer is connected with 

 either. We can hardly think otherwise than that the molecular changes 

 which sweep to and fro along the tangle of these fibrils (whose nutrition is 

 probably governed and hence whose functional activity is probably regulated 

 by the nuclear and scattered cells respectively) are influenced by or originate 

 the nervous impulses passing along the medullated fibres of the white matter ; 

 and hence we must conclude that either a continuity exists which has as yet 

 escaped detection, or, what is quite possible if not probable, that one fibril 

 can act upon another by simple contact or even at a distance. Further, 

 while the cell of Purkinje, with its large cell-body and nucleus, its conspicu- 

 ous axis-cylinder process and its other branched processes presents many 

 analogies with motor cells, such as those of the anterior horn of the spinal 

 cord, and raises the presumption that the impulses which move along its 

 axis-cylinder process proceed outward from the cell as motor or at least as 

 efferent impulses, we have no direct proof that this is so. And though it is 

 tempting to suppose that the other medullated fibres, which like the fibres 

 of a posterior root are lost in the gray matter, without the intervention of a 

 conspicuous cell, carry efferent impulses, we have as yet no proof of this. 

 All we can say is that the gray matter is connected in two different ways 

 with at least two sets of fibres, which probably therefore, have different 

 functions. 



We may here add the remark that the large body of the cell of Purkinje 

 lies, as indeed do the other nervous elements, in an appropriate space in 

 the bed of neuroglia. Between the surface of the cell and the wall of neur- 

 oglia is a space, generally so narrow as to be potential rather than actual, 

 but which may sometimes be considerable. Whether small or large it con- 

 tains lymph, and the cavity in which the cell lies is in connection with the 

 lymphatics of the brain. Each cell then lies in a lymph-space ; but we 

 merely mention the fact now ; we shall have to return to the matter when 

 we come to deal with the lymphatic and vascular arrangements of the brain 

 and spinal cord. 



The Cerebral Cortex. 



562. While the superficial gray matter of the cerebellum does not 

 differ strikingly as to its histological features in different regions, very con- 

 siderable differences are observed in different regions of the cerebral cortex. 

 A general plan of structure may perhaps be recognized, but as we pass from 

 one part of the cerebral surface to another we find modifications continually 

 taking place. We must content ourselves here with attempting a descrip- 

 tion of the general plan, followed by an indication of the more striking cha- 

 racteristics of certain regions. 



The cortical gray matter, having an average thickness of about 3 mm., 

 but varying considerably in different regions from 1.8 mm. in some parts of 



