THE MEDULLA OBLONG ATA. 39 



of the occipital bone, its dorsal or posterior surface is directly continued into that 

 of the pons, and lies in the fossa named the vallecula between the hemispheres of 



*^K. ^. .* , ~, ~ v . ..v.v , " , ^* v * V i* t j ""^*j , v/j corpora (juadrigeinina and pineal 

 + , the fourth ventricle ; 7, pons Varolii ; 8, medulla oblongata ; 9, cerebellum ; i, the olfactory 



t.Kfi -ricrlrf. nnt.ip nprvp TTT rio-Vif. tViiivl nprvp 



Fig. 29. RIGHT HALF OF THE BRAIN DIVIDED BY A VERTICAL ANTERo-PObTEKicm SECTION (from various 

 sources and from nature x >. (Allen Thomson. ) J 



] , 2, 3, 3a, 36, are placed on convolutions of the cerebrum ; 4, the fifth ventricle, and above it the 

 divided corpus callosum ; 5, the third ventricle ; 5', pituitary body ; 6, 

 gland ; + , the fourth ventricle ; 7, pons Varolii ; 8, me n 

 bulb ; ii, the right optic nerve ; in, right third nerve. 



the cerebellum. From its front and sides the sixth to the twelfth cranial nerves issue, 

 while the fifth nerve emerges from between the commissural fibres of the pons. 



The term medulla oblongata. as employed by Willis and Vieussens. and by those who 

 directly followed them, included the crura corebri and pons Varolii, as well as that part to 

 which by Haller first, and by most subsequent writers, this term has been restricted. 



Fig. 30. VIEW OF THE ANTERIOR SURFACE OF THE PONS VAROLII 



AND MEDULLA OBLONGATA, WITH A SMALL PART OF THE SPINAL 

 CORD ATTACHED. 



a, a, pyramids ; b, their decussation ; c, c, olives ; d, d, 

 restiform bodies ; e, external arciform fibres, curving round the 

 lower end of the olive ; /, fibres described by Solly as passing 

 from the anterior column of the cord to the cerebellum ; y, 

 anterior column of the spinal cord ; h, lateral column ; p, 

 pons Varolii ; i, its upper fibres ; v, v, roots of the fifth pair of 

 nerves. 



The combined mass of the medulla oblongata 

 and pons has an oblong or rhomboidal form, being 

 expanded in the middle, where it is continuous 

 with the crura cerebelli, and tapering towards the 

 spinal cord below and the mid -brain above. The 

 transversely coursing fibres of the cerebellum pro- 

 duce a considerable prominence (tuber annulare) on 

 the ventral surface of the upper or pontine part of the 

 mass ; these fibres are arched upwards so as largely 

 to conceal the crura cerebri from the ventral aspect. 



The length of the medulla 



oblongata from the lower part of the decussation of the pyramids to the pons is 



