202 ELEMENTS OF MAMMALIAN ANATOMY. 
spinal cord (Fig. 104). Likewise some of the fibers origi- 
nating in the cells of the cord, medulla, cerebellum, and 
basal ganglia terminate about the cells of the cortex. The 
cord, medulla, and cerebellum are connected with the higher 
brain centers by the fibers of the cerebral peduncles (Figs. 
93 and 104). Each peduncle is separted into two longi- 
tudinal parts by an elongated mass of gray matter, the 
substantia nigra. The dorsal part is known as the teg- 
mentum, while the ventral part is the crusta. 
The fibers of the brain are of three kinds—the commis- 
sural fibers, the projection fibers, and the association fibers. 
VV Pigg SS s ia 
= \ 
iI 
ch SS ie Swe, ES. é 
——— ZR mw Ep x 
= SJ WAYS 
==, Sale 
ee 
Fic. 104. DracrAm oF Cuier Fiber Tract oF THE MAMMALIAN BraIN. 
LateraL ASPECT. 
a, b, c, d, e, Fibers forming internal capsule; ac, anterior corpus quad- 
rigeminum; cb, direct cerebellar tract; cr, crossed pyramidal or 
chief motor tract; cs, cortico-pontine or secondary motor tract; m, 
middle peduncle of cerebellum; mg, nuclei gracilis and cuneatus; 1, 
decussation of crossed pyramidal tract; 0, optic thalamus; oc, optic 
chiasm; pc, posterior corpus quadrigeminum; pons, transverse fibers 
of pons Varolii; py,~pyramids formed by pyramidal tract; rn. 
nucleus ruber; s, antero-lateral cerebellar tract; sn, substantia 
nigra; sp, superior cerebellar peduncle; st, corpus striatum ; t, fibers 
of. the fillet or great sensory tract. 
The commissural fibers constitute the commissures of the 
brain previously described (Figs. 93, 95). In addition to 
these commissures, numerous other fibers cross to the 
