368 THE NERVOUS SYSTEM 



can be traced through the pons into the pyramid of the medulla. Carrying the dis- 

 section caudally, observe the decussation in the lower end of the medulla. 



83. Examine again the series of sections through the brain stem and color the 

 corticospinal tract red on the right side of your drawings. Draw the fibers from right 

 to left in the decussation (Fig. 237; pp. 136, 317). 



84. With red stipple indicate the somatic motor nuclei on the left side of your draw- 

 ings. Which nuclei are they? (See pp. 170-173.) 



CEREBELLAR CONNECTIONS 



85. The inferior peduncle has already been studied and the cortico-ponto-cerebellar 

 path has been dissected. Review this path in your sections. Color the corticopontine 

 tracts of the left side brown ( Fig. 117). Indicate the nuclei pontis of the left side by 

 brown stipple. Draw the transverse fibers of the pons from the left nuclei pontis to 

 the right brachium pontis (Fig. 106; pp. 147-149). 



86. In the left lateral half of the sheep's brain follow the brachium conjunctivum 

 by dissection into the tegmentum of the mesencephalon and note its decussation 

 beneath the inferior colliculus. In your sections trace it rostrally, noting its decus- 

 sation and termination (Figs. 110, 112, 114-116). Indicate it in brown on your 

 drawings, beginning on the right side and tracing it through the decussation to the left 

 red nucleus. Stipple both red nuclei with brown. (See pp. 159, 326.) 



87. The Rubrospinal Tract. Trace the rubrospinal tract from the red nucleus 

 through the ventral tegmental decussation (Fig. 116) and the reticular formation of the 

 brain stem. In the reticular formation it occupies a position ventromedial to the 

 nucleus of the spinal root of the trigeminal nerve (Figs. 115, 234; pp. 161, 326). Color 

 it brown on the left side of your drawings. 



THE RETICULAR FORMATION 



88. Study the reticular formation in the various sections. Of what is it composed? 

 How many kinds of internal arcuate fibers can you find? What is the source of the 

 longitudinal fibers of the reticular formation? Locate the tectospinal tract and in- 

 dicate it in black on the left side of your drawings. (See pp. 144, 145). 



89. The Fasciculus Longitudinalis Medialis. Examine all nine sections, and enter 

 this bundle in black on both sides of your drawings. What is the source of its fibers 

 and what is its function? (See Fig. 109; pp. 152, 162). 



PROSENCEPHALON 



90. With a sharp brain knife divide the human brain exactly in the median sagittal 

 plane, and then cut the left cerebral hemisphere into a series of frontal sections. The 

 planes of the sections should pass through (1) the rostrum of the corpus callosum, 

 (2) the anterior commissure, (3) the mammillary body, (4) the habenular nucleus, 

 (5) the pineal body and the splenium of the corpus callosum (Figs. 186-190). 



91. Take the right half of the sheep's brain and make such dissections as may be 

 necessary to secure a good preparation of the structures indicated in Fig. 84. Begin 

 at the rostral angle of the fourth ventricle and follow the cerebral aqueduct, tearing 

 away with tissue forceps any parts of the left lateral wall which have not been cut away. 



