THE MAMMALIAN NEKVOTJS SYSTEM 113 



to work out the cortico-spinal (pyramidal) tract. Although 

 functionally a motor and therefore a descending tract, it can 

 more easily be traced from the oblongata upward to the higher 

 centers. It appears as an eminence (pyramis) on the ventral 

 surface of the oblongata below the pons near the midline (cf . 

 Section 95). Its fibers interdigitate with those of the pons, 

 through which the cortico-spinal tract can be traced. It can 

 then be followed along the ventral surface of the mesencepha- 

 lon through the pedunculus cerebri into the internal capsule. 

 These fibers arise from the cortical neurons of the superior 

 frontal gyrus; see King ('11) and Simpson and King ('11). 



139. Internal capsule. From the reference books master 

 the topographic relations of the functional systems of fibers in 

 the internal capsule. For the connections of these tracts in the 

 human brain see the following: Barker ('01), pp. 666-746 and 

 875-1048; Barker ('16), Fig. 591, p. 442; Cunningham ('15), 

 Figs. 567-573, pp. 638-643, also account on p. 642; Herrick 

 ('18), Figs. 45, 79, 80, 81, 83; Morris ('14), Figs. 692-700, pp. 

 880-888; Piersol ('16), Figs. 1009-1012, pp. 1170-1174; 

 Spalteholz ('09), Fig. 745; Villiger ('12), Figs. 128-136, pp. 

 136-143. 



140. The dissection of the cerebrum of the sheep's brain, as 

 outlined in the preceding sections, can be completely carried 

 out on one lateral half of the brain. The other half of the 

 specimen can profitably be used for a repetition of the dissec- 

 tion, or it may be cut into a series of transverse or longitudinal 

 slices, in each of which some of the structures already observed 

 may be identified. 



Some members of the class may slice this hemisphere in the 

 transverse plane, others in the horizontal, and others in the 

 sagittal, and these specimens may be compared by all members. 

 Compare these sections with transverse sections of the human 

 brain to be supplied by the instructor. Poorly preserved 

 brains which are of small value for dissection by the method of 

 teasing will give excellent gross sections for this study. In 

 these sections look particularly for the continuation of the 

 cerebral peduncle into the internal capsule. Make an especial 

 study of the relations of the internal capsule to the adjacent 

 structures, noting how the corpus striatum is made up of the 



