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TEXT-BOOK OF PHYSIOLOGY. 



the sixth, the seventh cranial nerves. Some of the groups are the 

 sensor end-nuclei of the fifth and eighth cranial nerves. 



The crura cerebri comprise that portion of the central nerve sys- 

 tem situated between the pons below and the cerebrum above. They 

 are composed of strands of nerve-fibers which are divided, as shown 

 on cross-section, into a ventral and a dorsal portion by a crescentic 

 shaped layer of gray matter, the substantia nigra (Fig. 214). Of the 

 fibers which compose the ventral portion of each cms, the crusta 

 or pes y the larger part is continuous below, through the longitudinal 

 fibers of the pons, with the pyramid of the medulla and the pyramidal 

 tract; above they assist in the formation of the internal capsule. 



On the inner and on the outer 

 side of each crusta there is a 

 bundle of fibers derived from 

 the frontal, and from the 

 temporal and occipital por- 

 tions of the cerebrum respec- 

 tively. These fibers are con- 

 nected directly with the nuclei 

 pontis and indirectly with 

 the cerebellum of the same 

 and opposite sides. The 

 fibers which compose the 

 dorsal portion, the tegmentum, 

 are continuous with those 

 which pass upward from the 

 medulla and pons, e. g., the 

 fillet, both mesial and lateral, 

 the formatio reticularis, the 

 posterior longitudinal bundle, 

 and, in addition, the fibers of 

 the superior peduncles of the 

 cerebellum. Above, the fibers terminate largely in collections of gray 

 matter at the base of the cerebrum. 



The aqueduct of Sylvius is a short narrow canal which connects 

 the cavity o t the iourtn with the cavity of the third ventricle. It is 

 lined by the ependyma and surrounded by a layer of gray matter 

 continuous with that forming the floor of the fourth ventricle. In 

 that portion of the gray matter lying beneath or ventral to the aqueduct 

 there are groups of nerve-cells which give origin to axons which unite 

 to form the third and fourth cranial nerves. 



FIG. 214. SCHEME OF TRANSVERSE SEC- 

 TION OF THE CEREBRAL PEDUNCLES. 

 CQ. Corpora quadrigemina. Aq. Aque- 

 duct, p.l.b. Posterior longitudinal bun- 

 dle. F. Fillet or lemniscus. RN. Red 

 nucleus. SN. Substantia nigra. III. 

 Third nerve. Py. Pyramidal tracts. 

 FC. Fronto-cerebellar; and TOC, tem- 

 poro-occipital fibers of the crusta. CC. 

 Caudate-cerebellar fibers in upper part 

 of crusta. (After Wernicke and Cowers,} 



