1878.] 



of the Motor Area of the Brain. 



41 



more distant grouping. It will be seen in traversing the full depth 

 of this layer (Plate 1, Third Layer) that the cells almost uniformly 

 increase in size from above downwards, yet small pyramidal bodies, no 

 larger than those at the commencement of the series, are found occa- 

 sionally at all depths, side by side with the larger nerve-cells. The 

 configuration of these cells is by no means uniform. They often assume 

 the pyriform rather than the truly pyramidal form, having their 

 larger basal extremity marked by numerous dentations, from whose 

 projecting points delicate branches are thrown olf on all sides. Their 

 apical process is directed radially to the surface of the cortex, and can 

 be traced up into its second layer. Each cell contains a nucleus 

 and a distinct nucleolus. The basal or axis-cylinder process is rarely 

 seen, as it is necessarily divided, in most cases, by the oblique direction 

 which it takes to reach the radiating fibres of the medulla. These 

 cells vary greatly in dimensions : those in the uppermost regions of 

 this stratum measuring 12/* by 8/t, their nucleus being 7/i by 5/t ; 

 whilst those in parts bordering upon the subjacent layer average 22/i 

 in length, and the largest cells even attain a size of 41/t by 23/*. 



Fourth Layer. — We have now entered upon highly debatable ground, 

 including the chief topic we have proposed for consideration. Much 

 confusion appears to have prevailed with regard to the characters and 

 relationships of this and the subjacent layers. Thus, Meynert* 

 describes the fourth layer as constituted of irregular angular cells, 

 forming a stratum immediately superincumbent on his fifth layer of 

 spindle-cells. Baillarger, on the other hand, enumerates six cortical 

 layers, of which Meynert's angular and spindle-cells form his fourth 

 and sixth respectively. After considering fully the views of various 

 writers on this subject, we find ourselves unable to agree with most of 

 them regarding this type of lamination. The layer immediately 

 beneath the third undoubtedly consists of angular cells which in size, 

 form, and branchings are accurately described by Meynert. They 

 resemble, on a small seal?, transverse sections of large pyramidal 

 cells, numerous branches being given off from all sides of the cell, and 

 rarely are they seen extended radially towards the surface of the 

 cortex. Now we find this stratum of angular cells intersected by a layer 

 of immense ganglionic cells, which run about midway through the 

 stratum, and it is distinctly affirmed that these angular cells are found 

 freely above and heloiv this important formation (Plate 1, Fourth Layer). 

 On turning our attention more especially to these ganglionic cells, 

 we find that they differ very materially from any of the elements 

 already described. The enormous dimensions to which they attain, 

 averaging 71/t in length by 35/* in breadth, stamp them as the most 

 notable objects in the whole depth of the cortex, whilst in special cells 

 the not unusual length of 126/*, shows that they occasionally rival even 



* Op. cit., p. 389. 



