THE FOURTH VENTRICLE. 



49 



but it is somewhat thickened by the addition of white nervous matter before 

 reaching the lateral boundaries of the floor. This thickening is left as a slightly 

 prominent and often ragged membrane when the epithelium of the roof of the 



C 



i 



Fig. 41. DIAGRAMS TO SHOW THE SITUATION OF THE CHIEF NERVE-NUCLEI IN THE MEDULLA OBLONGATA 



AND PONS NEAR THE FLOOR OF THE 4lH VENTRICLE. TWICE THE NATURAL SIZE. 



A, from behind ; B, profile view of the right half, the medulla and pons being supposed to be trans- 

 parent. The efferent or motor nuclei are shaded with oblique lines, the afferent or sensory nuclei with 

 dots. In A the efferent or motor nuclei are represented on the, right side only, the afferent or sensory 

 on the left. ///, IV, oculomotor and trochlear nucleus; V.d, descending root of the fifth 

 nerve ; V. s, so-called sensory nucleus of the fifth ; V.a, ascending root of the fifth ; V.m, motor 

 nucleus of fifth nerve ; VI, nucleus of abducens ; VII, nucleus of facial ; n. VII, root of facial curving 

 round abducens nucleus ; VIII, inner or dorsal nucleus of auditory ; VIII 1 , outer or ventral nucleus of 

 auditory ; IX, X. vago-glossopharyngeal nucleus ; n.a., nucleus ambiguus, accessory or efferent vago- 

 glosso-pharyngeal nucleus ; XI, nucleus of spinal accessory ; XII, nucleus of hypoglossal ; XII', 

 issuing roots of hypoglossal. 



ventricle is torn off with the pia mater. It commences at the apex of the clava, 

 and accompanies the lateral boundary for a short distance ; then turns over the 

 surface of the restiform body and terminates close to the place whence the roots 

 of the vagus and glosso-pharyngeal nerves issue. It is termed the tc&nia or ligula- 

 (fig. 44, t), and its upper transverse part forms the lower boundary of the lateral 



VOL. III. K 



