SURFACES. 



289 



stretches between the two restiform bodies, and roofs over the 

 inferior part of the fourth ventricle. That is the roof epithelium. 

 It is continuous with the surface layer of the ependyma lining the 

 fourth ventricle. By it the posterior surface is completed. 



The roof epithelium (Figs. 90 and 91), seen in the mid-dorsal 

 surface of the medulla, is of triangular shape; its base is attached 

 to the inferior medullary velum of the cerebellum; its apex, which 

 is directed downward, terminates at the obex and covers the 



Inferior quadrigeminal 



colliculus 



Fourth nerve 



Superior medullary 

 velum 



Brachium 

 conjunct! vum 



Brachium 

 pontis 



Restiform body 



Taenia 



Epithelial roof of 

 fourth ventricle 



Cuneate tubercle' 



Clava 



Tuberculum cinereum 



Frenulum veli 

 LateraL'fillet 



Inferior medullary 

 velum 

 Chorioid plexus 



Median aperture 

 (Magendi) 



Obex 



Fig. 91. Roof and lateral walls of fourth ventricle, and its chorioid plexuses. 

 (After Morris's Anatomy.) 



inferior angle of the fourth ventricle; and, laterally, it is attached 

 to the clava, the cuneate funiculus and the restiform body. The 

 line of attachment to the restiform body runs, first, obliquely 

 upward and outward; and then, transversely outward, inferior 

 to the lateral recess. The borders of the epithelial lamina become 

 thickened by .the addition of neuroglia, and are in continuity 

 with the ependyma of the ventricle. The thickened apex of the 

 epithelial lamina is called the obex. With the pia mater investing 

 19 



