488 



THE ORGANS 



triangular area with an angle directed into the lateral recess marks 

 the area occupied by the nuclei of the acoustic nerve {area acustica). 

 Still further cephalad near the median line are eminences indicating 

 the positions of the nucleus abducentis and genu facialis. The roof 

 of the fourth ventricle is formed by the thin plexus chorioideus and 

 the cerebellum. (Fig. 332.) 



The Pons is a mass of fibres and gray matter extending across the 

 ventral surface of portions of mid- and hindbrain. The term is often 



Corp. mamillaria 

 Corp. pineale 



Colliculus sup. 



ColHculus inf 



Emin^ntia med 



Olive (in A) 



Area acustica (in B) 



Eminentia med. 



Ala cinerea 



Clava 



Dec. pyramids \ 



Tub. cuneatum / 



Tub. cinereum 



Fig. 318 

 Fig. 317 



Fig. 2>i-- — -Ventral (A) and dorsal (B) views of part of Brain Stem (cerebellum 

 removed). Structures named at the left are indicated by their reference lines running to 

 an X. On the right are named the figures showing transverse sections through the brain 

 at the levels indicated by the reference lines. The level for Fig. 357 is not quite 

 accurately indicated. 



used to include the whole of the basal part of the brain thus covered 

 by the pons. It is better, however, to restrict it to the pons itself. 

 The part of the hindbrain dorsal to the pons, which is the continua- 

 tion forward of the medulla, may be included in the term tegmentum 

 of the hindbrain. 



The Cerebellum is described on p. 513. 



r TECHNIC 



The technic of the medulla (and the rest of the segmental brain) is the same 

 as that of the cord (page 477). Transverse sections should be cut through the 

 following typical levels, stained by Weigert's method (page 2)i), and mounted 

 in balsam: 



