THE CEREBRAL CORTEX 



73 



deeper layer of the cortex from the other layers, and have considered its cells as association 



rather than projection cells. The fibres of 



this layer are seen to pass in all possible 



directions, intermingling with the neuraxons 



of the other layers, which descend through 



the layer to enter the white matter be- 

 neath. 



An attempt has been made to put 



together the various elements of the cor- 

 tex here described in a scheme or diagram 



(Fig. 10) which may convey to the mind a 



picture of their mutual relation. Each va- 

 riety of cell which has been described and 



photographed in the plates is reproduced 



and is given its proper size and position 



relatively to the other cells. The course of 



the fibres within the cortex is also shown, 



with their probable termination so far as 



actually determined. Fibres r are supposed 



to be glia fibres forming a part of the 



glia framework supporting the cortex. The 



various systems of fibres entering and terminating in the cortex are not shown. 



The neuraxons of all these cells are 

 shown, making up the white matter beneath 

 the gray, and giving off in their course 

 collaterals which pass in various directions. 

 The various neuraxons making up the 

 white matter beneath the cortex have been 

 classified by anatomists in accordance with 

 their final destination. 



There are (i) projection fibres, which pass 

 through the centrum ovale into the internal 

 capsule and thence to some of the masses 

 of gray matter in the basal ganglia, me- 

 dulla, or spinal cord. These bring the 



FIG. ii. 



FIG. II. The projection tracts joining the cortex with lower nerve centres. 

 Sagittal section showing the arrangement of tracts in the internal capsule. 



A, Tract from the frontal lobe to the pons, thence to the cerebellar 

 hemisphere of the opposite side. B, motor tract from the central convolu- 

 tions to the facial nucleus in the pons and to the spinal cord; its decussation 

 is indicated at K. C, sensory tract from posterior columns of the cord, 

 through the posterior part of the medulla, pons, crus, and capsule to the 

 parietal lobe. D, visual tract from the optic thalamus (OT) to the occipi- 

 tal lobe. E, auditory tract from the corp. quad. post, to which a tract 

 passes from the VIII. N.. nucleus (f) to the temporal lobe. F, superior 

 cerebellar peduncle. G, middle cerebellar peduncle. H, inferior cerebellar 

 peduncle. CA 7 , caudate nucleus. CQ, corpora quadrigemina. Vt, fourth 

 ventricle. The numerals refer to the cranial nerves. 



FIG. 12. 



FIG. 12. The association fibres. 



A, Between adjacent convolutions. B, between frontal and occipital 

 areas. C, between frontal and temporal areas, cingulum. D, between frontal 

 and temporal areas, fasciculus uncinatus. E, between occipital and temporal 

 areas, fasciculus longitudinalis inferior. CN, caudate nucleus. OT, optic 

 thalamus. 



