Xrri.KI OF THE CRANIAL NERVES. 



7SS 



and is named the "/<' a/>< / " (fig. 287, ac) : it corresponds to the aU daerat, 

 nucleus of the vagus nerve. On the outer side of the fovea the 

 surface is elevated over the principal nucleus of the auditory nerve, 

 forming the auditory tubercle (at). 

 which is crossed by the auditory 



In the upper half of the floor of 

 the ventricle there may be seen, on 

 the inner side of the superior fovea, 

 a rounded elevation of the fasciculus 

 'reduced by the nucleus of the 

 sixth nerve. And lastly, above the 

 superior fovea is a narrow, slightly 

 -ed area of a bluish colour (locus 

 cjeruleus). caused by a deposit of very 

 dark grey substance (substantia ferru- 

 ginea) beneath the thin surf ace -layer. 



The fourth ventricle communicates 

 above with the third ventricle through 

 the aqueduct of Sylvius, and with the 

 subarachnoid space below through an 

 ftpertare (foramen of Majendie) in the 

 ia mater between the cerebellum and 

 medulla oblongata. Below, also, it 

 opens into the central canal of the cord. 

 It is lined by ependyma, the epithe- 

 lium of which is continued over the 

 pia mater in the roof, and prolonged 

 upwards and downwards into the 

 canals leading from the ventricle. 



Projecting into the lower half of 

 the ventricle is a vascular fold on 

 each side, the clioroifl pl>. ,->/*, similar to 

 the body of the same name in the 

 lateral and third ventricles. It is 

 attached to the inner surface of the 

 pia mater which closes the ventricle 

 between the medulla and the cere- 

 bellum, and extends from the point 

 of the calamus scriptorius to the ex- 

 tremity of the lateral recess of the 

 cavity. It receives branches from the 

 inferior cerebellar artery. 



FIG. 287. DIAGRAM SHOWING 

 THE POSITION OF THE NERTE- 

 NUCLEI NEAR THE FLOOR OF 



THE FOURTH VENTRICLE. THE 



ROMAN NUMBERS INDICATE 

 THE NUCLEI OF THE CORRE- 

 SPONDING NERVES. 



Vd. Nucleus of the descend- 

 ing root. 



V?. Motor nucleus, and 



Vs. Sensory nucleus of the 

 fifth nerve. 



VIIIo. Outer, and 



VIII?'. Inner auditory nucleus. 



XI. Upper part of the spinal 

 accessory nucleus. On the left 

 side : 



cq. Position of the corpora 

 quadrigemina. 



nt. Auditory tubercle. 



ac. Ala cinerea. 



The floor of the fourth ventricle 



is covered by a layer of 'grey matter, which is continuous below 

 with the grey commissure of the cord, and above with the grey 

 substance of the aqueduct. 



NUCLEI OF CRANIAL NERVES (fig. 287). In the dorsal portion 

 of the medulla oblongata and pons are situate the collections of 

 nerve-cells from which many of the cranial nerves take their origin. 



Choroid 

 plexus of 

 cavity. 



Grey layer 

 of floor. 



Nerve 

 nuclei in 

 and near 



