72 



and cuneate funiculi, {b) the restiform body. Note the relation of 

 the restiform body and the pons to the peduncles of the cerebellum. 

 In examining the following sections, whenever one of these struct- 

 ures is mentioned, examine the gross preparations and ascertain the 

 plane of the section. 



164. Decussation of the pyramids. Cat. Transection of 

 the oblongata at the level of the decussation of the pyramids. 



3% and 5% potassium dichromate ; collodion ; Weigert's hema- 

 toxylin stain (§ 137) ; sections u. Now in 95% alcohol. 

 Clear and mount in balsam (alkaline). 



Recall the positions in the myel occupied by the following 

 tracts : (r) the crossed and direct pyramidal tracts, (2) the direct 

 cerebellar, (j) the funiculi gracilis and cuneatus composing the 

 dorsal column. In this section will be seen the decussation of the 

 fibers that will constitute the crossed pyramidal tracts in the myel 

 from their position on the ventral side (pyramids) to the lateral 

 column of the myel. Recognize the dorsal and ventral columns, 

 the substantia gelatinosa Rolandi, the nucleus gracilis. I,aterad of 

 the cap of gelatinosa Rolandi is the ascending (sensory) root of the 

 Vth cranial nerve ; ventrad of this, the fibers of the direct cerebellar 

 tract. . 



165. Decussation of the lemniscus. Transection 

 of the oblongata, through the nuclei gracilis and cuneatus and the 

 pyramids (caudal part). Weigert's hematoxylin method (§ 137) ; 

 now in 95% alcohol ; sections fji. Clear and mount in alkaline 

 balsam. 



At this level, slightly cephalad of 153, the decussation of the 

 pj'ramidal tracts has not yet begun, the gracile nucleus has en- 

 larged and the cuneate nucleus has appeared. Recognize these 

 features and, in addition, the decussation of fibers from these nuclei 

 to form the lemniscus. Note the pyramid's, the diminished funi- 

 culus gracilis (what has become of the fibers?); the dorsal cornu 

 and substantia gelatinosa Rolandi ; can you identify the ventral 

 cornu ? Note increased distinctness of the ascending root of the Vth 

 ■ and the direct cerebellar tract. The nuclei of the Xllth and Xth 

 nerves and the fibers of the Xllth passing to their exit may also 

 be seen. The section may be slightly cephalad or caudad of the 

 level desired for this preparation ; which is it ? 



