474 



TEXT-BOOK OF PHYSIOLOGY. 



THE BASAL GANGLIA. THE CORPORA STRIATA AND OPTIC 



THALAMI. 



The basal ganglia surmount the crura cerebri, but are only 

 made visible by removal of the cerebrum (Fig. 215). 



FIG. 215. DISSECTION OF BRAIN, FROM ABOVE, EXPOSING THE LATERAL FOURTH 

 AND FIFTH VENTRICLES WITH THE SURROUNDING PARTS. . a. Anterior part, 

 or germ of corpus callosum. b. Corpus striatum. b f . The corpus striatum of 

 left side, dissected so as to expose its gray substance, c. Points by a line to the 

 taenia semicircularis. d. Optic thalamus. e. Anterior pillars of fornix divided; 

 below they are seen descending in front of the third ventricle, and between them 

 is seen part of the anterior commissure; in front of the letter e is seen the slit-like 

 fifth ventricle, between the two laminae of the septum lucidum. /. Soft or middle 

 commissure; g is placed in the posterior part of the third ventricle; immediately 

 behind the latter are the posterior commissure (just visible) and the pineal 

 gland, the two crura of which extend forward along the inner and upper margins 

 of the optic thalami. h and i. The corpora quadrigemina. k. Superior crus 

 of cerebellum. Close to k is the valve of Vieussens, which has been divided so 

 as to expose the fourth ventricle. /. Hippocampus major and corpus fimbria- 

 tum, or taenia hippocampi, m. Hippocampus minor, n. Eminentia collateral's. 

 o. Fourth ventricle, p. Posterior surface of medulla oblongata. r. Section 

 of cerebellum, s. Upper part of left hemisphere of cerebellum exposed by the 

 removal of part of the posterior cerebral lobe. (Hirschfeld and Leveille.) 



The corpora striata are two large ovoid collections of gray and 

 white matter situated at the base of the cerebrum. The larger portion 

 of each body is embedded in the cerebral white matter, while the 



