THE MAMMALIAN NERVOUS SYSTEM 81 



on the ventral surface, the pyramid, from which the tract 

 receives its name. Its fibers can be followed into the sub- 

 stance of the pons. Here, as the sections are followed upward, 

 the fibers of the cortico-pontile tracts are added to them, so 

 when they emerge upon the ventral surface of the cerebral 

 peduncle above the pons, the pyramidal fibers form only the 

 middle part of the basis pedunculi, with cortico-pontile fibers 

 on each side of them. 



Enter the pyramidal tract in the sketches, consulting Herrick 

 ( J 18), Fig. 75, for its position in the cerebral peduncle. The 

 following references are also suggested: Bailey ('16), Fig. 331, 

 p. 486; Cunningham ('15), Fig. 480, p. 545; King ('11); Morris 

 ('14), Fig. 664, p. 841, and Fig. 706, p. 897; Piersol ('16), Fig. 

 1026, p. 1187; Rauber-Kopsch ('12), Figs. 263, 264, pp. 276, 

 277; Toldt ('09), Fig. 1216, p. 790; Fig. 1229, p. 800; Villiger 

 ('12), Figs. 176, 179, 181, 182. 



95. Dissection of the pyramidal tract. The pyramidal tract 

 can readily be dissected in the brains of the sheep and of man. 

 If only one human brain is to be dissected and it is desired to 

 make the optional dissections, this tract should not be exposed 

 in this specimen at this time (see Section 138). 



On the right half of the brain of the sheep (see Fig. 8) locate 

 the pyramid on the ventral surface below the pons. Strip the 

 pons fibers back from the cut median surface for a short dis- 

 tance so as to expose the longitudinal pyramidal fibers dorsally 

 of them. In the sheep the pyramidal fibers will be found to 

 interdigitate with those of the trapezoid body and one or the 

 other of these systems will have to be partially destroyed to 

 expose the other. In following the pyramidal tract spinal- 

 ward, careful teasing will separate its fibers as far down as 

 their decussation, below which they can no longer be dissected. 

 For their spinal course see King ('11). 



From the pons upward the pyramidal tract can be dissected 

 through the cerebral peduncle, the number of associated cortico- 

 pontile fibers being much less than in man. The further dis- 

 section of the pyramidal tract through the cerebral hemisphere 

 should be deferred (see Sections 138 and 150). 



There are many descending systems besides the pyramidal 

 tracts; for an excellent summary of these see Rauber-Kopsch 

 ('12), pp. 275-292. 



