STRUCTURE OF THE LOBES OF THE CEREBRUM. 387 



length of 40 ju. If we remember that the anterior roots of the 

 spinal cord, at their origin in the anterior cornua, are connected 

 with elements which, through the slenderness of their bodies, the 

 gradual transition of these bodies into the protoplasm of the pro- 

 cesses, and the greater number and size of the latter, are sharply 

 differentiated from the cells in which the posterior roots originate 

 in the interspinal ganglia, these being tumid, and provided 

 with few and attenuated processes, an affinity in point of form 

 is at once seen between the pyramids of the cortex and the 

 former, which is common also to the cells of origin of all 

 motor cerebral nerves, and permits an analogy to be drawn 

 in regard to the significance of the pyramids of the cortex. 

 The larger elements of the third layer deserve the special 

 name of the formation of the cornu Ammonis, as they are 

 the only morphological structures that are found in it. 



The form of a simple pyramid (fig. 235, a) which is most 

 frequently seen is deceptive. The true form (fig. 235, 6) is 

 that of a spindle, the axis of which lies in the direction of the 

 radiating projection-fibres of the medullary portion of the con- 

 volution, and gives off an external strong and, according to 

 Max Schultze (vol. i., chap, iii., p. 183), branched process (fig. 

 235, a), which runs outwards ; and an internal more slender 

 process directed towards the medulla of the convolution, and 

 which, remaining, according to Koschewnikoff, undivided, forms 

 the axis-cylinder process of Remak, M. Schultze, and Deiters. 

 The fusiform body gives off laterally also from five to seven 

 processes, which, like the apical process, form demonstrable 

 anastomoses. If we make use of the term "pyramid of the 

 cortex," then the three kinds of processes may be respectively 

 designated (1) the process of the apex, (2) the process of the 

 centre of the base, and (3) the process of the basal angles. 



The central basal process, on account of the infrequency with which 

 it is seen in Man, has been regarded as a monstrosity in him by Arndfc, 

 whilst he held it to be of constant occurrence in the Bat and Sheep. 

 It is the more rarely seen because, being the process which enters 

 the medulla, its direction is dependent on the angles formed by the fasci- 

 culi of the latter, which by no means form a straight line with the apical 

 process of the pyramid. In sections, therefore, made parallel to the 

 cleavage of the cortex, which is formed by the radiating lines of the apical 



c c 2 



