THE BRAIN AND ITS MEMBRANES. 



715 



to the posterior median fissure, and approaching the surface forms a prominence 

 which is covered over by a very thin layer of white matter derived from the 

 funiculus cuneatus. Its most prominent part is its upper end, which is called 

 the tubercle of Rolando. 



The funiculus cuneatus is the direct continuation upward of the postero- 

 lateral column of the cord L e. its white fibres are derived from this region of 

 the cord. The fibres end in the gray matter which forms the so-called nucleus 

 of this column : this nucleus, at first narrow, gradually enlarges, and produces, 

 externally, the eminence mentioned above as the tuberculum cuneatum. 



The funiculus gracilis is the direct continuation upward of the posterior 

 median column of the cord. It consists entirely of white fibres, which are 

 continuous with those of this region of the cord. Like the funiculus cuneatus, 

 its fibres end in its so-called nucleus, which produces externally the prominence 

 mentioned above as the clava. 



THE UPPER, OPEN, OR VENTRICULAR PART OF THE MEDULLA. The gray 

 matter, as in the lower part, contributes to form a formatio reticularis, but this 

 is confined chiefly to the anterior and lateral " areas." In the posterior " area " 

 the gray matter, dorsally, is found to consist mainly of numerous individual 

 masses of cells or nuclei scattered among fibres 

 which are mostly longitudinal, while ventrally there 

 is a small amount of reticular formation. 



There are also other individual nuclei found in 

 the anterior and lateral areas. 



Gray Matter of the Anterior and Lateral Areas. 

 This is chiefly seen in the formatio reticularis, 

 dorsal to the pyramids and olives (Figs. 417 and 

 421). It is practically a continuation upward of 

 the same structure in the closed portion of the bulb. 

 In the anterior area the nerve-cells are infrequent 

 and small as compared with those in the lateral 

 area, Diving a whiter appearance on section. Hence 



, p i /> i v- u J.U 



that part of the formatio reticularis which is m the 

 anterior area is called the formatio reticularis alba, 

 while that of the lateral area is known as the formatio reticularis grisea. Just 

 anterior to the latter in fact, projecting into the olive, the prominence of which 

 it produces is a large isolated nucleus, the nucleus of the olivary body (Figs. 

 417. 420, and 421). This is really a hollow capsule, with an opening or hilum 

 directed toward the middle line. White fibres extend into and proceed out of 

 this capsule through the hilum, constituting the so-called olivary peduncle. On 

 section the wall of this capsule is seen to be wavy and irregular in outline: hence 

 the nucleus is often called the corpus dentatum or dentate nucleus of the olivary 

 body. Microscopically, the wall of the nucleus appears to be made up of neur- 

 oglia, in which are placed small multipolar nerve-cells. From the surface this 

 nucleus is not seen, being concealed by the fibres of the olive. 



In addition to the main olivary nucleus there are two accessory olivary nuclei 

 (Fig. 417), "inner" and "outer" respectively. The former is in the anterior 

 area, dorsal to the pyramid ; the latter in the lateral area, dorsal to the main 

 nucleus. 



Gray Matter of the Posterior Area (Figs. 417, 420, and 421). Inferiorly, 

 close to the lower half of the bulb, are seen the upper ends of the nuclei of the 

 funiculus cuneatus and gracilis. The bulk of this gray matter, however, is 

 observed, on section, to consist of numerous nuclei, ventral and mesial to which 

 is a small area of reticular formation. 



The Nuclei (Fig. 417). It must be remembered that the region now being 

 considered is just ventral to the floor of the fourth ventricle and the restiform 

 bodies. In other words, owing to the " widening-out " process which has occurred 

 in this part of the medulla the posterior " area " has dorsal to it, laterally, the 



Pyramid 



FIG. 421. Transverse section of the 



upper part of the medulla X f. (Ge- 



