CHAP, ii.] THE BRAIN. 1027 



special regions are of very large size, J20 //, by 50 fj, and have 

 been called 'giant cells.' 



The features of a ' large pyramidal ' cell are very characteristic. 

 Such a cell appears in a well prepared vertical section of the 

 cortex as an elongated isosceles triangle placed vertically, with 

 the base looking towards the underlying white substance and the 

 tapering apex pointing to the surface. The cell substance is 

 finely granulated or nbrillated, the fibrillae sweeping round in 

 various directions ; it not unfrequently contains pigment. In 

 the midst of this cell-substance rather near the base lies a large 

 clear conspicuous round or oval nucleolated nucleus. At the base 

 the cell-substance is prolonged into a number of processes. One 

 of these, generally starting from about the middle of the base, 

 runs for some distance without dividing, and soon acquiring a 

 medulla may be recognized as an axis cylinder process ; the fibre 

 to which it gives origin sweeps with a more or less curved course 

 into the subjacent white matter. In some instances the axis 

 cylinder process, by a T division like that seen in a ganglion of a 

 posterior root ( 97) gives rise to two fibres, one of which may 

 take a horizontal direction; in some regions of the cortex, the 

 occipital for instance, the axis cylinder process is said to give rise 

 by division to several fibres. The other processes from the base, 

 especially those from the angles of the triangle, rapidly branch 

 into fine fibrils which are soon lost to view in the ground 

 substance. The apex of the triangle is also prolonged into a 

 process, which giving off fine lateral branches, makes as it were 

 straight for the surface, but ultimately branching into fine fibrils 

 is lost to view at some distance from the body of the cell. The 

 cell lies in a cavity of the ground substance which it appears 

 normally to fill, but from the walls of which it sometimes shrinks, 

 developing between itself and the wall of the cavity a space which 

 may contain not only lymph but occasionally leucocytes. In 

 prepared specimens the retraction within its cavity of the arti- 

 ficially shrunken cell may be often observed. 



The 'small pyramidal' cells have much the same features; 

 that is to say the cells are characterized by their pyramidal 

 form, though this is naturally not so distinct, by their vertical 

 position, and by the possession of branching processes which are 

 lost in the molecular ground substance ; the presence however of a 

 midbasal axis-cylinder process has not been clearly demonstrated. 



Other nerve cells are more like the ordinary nerve cells of the 

 spinal cord and of the internal cerebral grey matter; they are 

 branched cells of irregular, not of pyramidal form and for the 

 most part small, 18 //, by 10 JJL. They may be characterized by 

 the relative large size (7 /z) of the nucleus, and do not possess 

 an axis cylinder process ; at least such a process has not yet 

 been demonstrated. They are frequently spoken of as ' angular ' 

 cells. 



