48 



THE MEDULLA. OBLONGATA AND POXS VAROLII. 



is marked dorsally by three or four flat transverse grey laminse, Avith intervening 

 sulci, which together constitute the lingula (fig. 39, Ing}. This is continued 

 laterally into the grey cortex of the cerebellum, while the subjacent white substance 

 of the velum is in direct continuity with the central white matter of the cerebellum, 



cbl 



S.CJ) 



Fig. 39. POSTERIOR AND LATERAL VIEW OP 



THE MEDULLA OBLONGATA, FOURTH VENTRICLE 

 AND MESENCEPHALON. (E. A. S. ) NATURAL 

 SIZE. 



The cerebellum and inferior medullary velum, 

 and the right half of the superior medullary 

 velum, have been cut away, so as to expose the 

 fourth ventricle. 



p.n., line of the posterior roots of the spinal 

 nerves ; p.m./., posterior median fissure ; f.g., 

 funiculus gracilis ; cZ. , its clava ; f.c. , funiculus 

 cuneatus ; /. R. , funiculus of Rolando ; r. 6. , 

 restiform body; c.s. , lower end of the fourth 

 ventricle (calamus scriptorius) ; I, section of the 

 ligula or twnia ; part of the choroid plexus is 

 seen beneath it ; J.r., lateral recess of the 

 ventricle ; str, striae acusticae ; ?'./., inferior 

 (posterior) fovea ; ./., superior (anterior) 

 fovea ; between it and the median sulcus 

 is the funiculus teres ; cbl, cut surface of 

 the left cerebellar hemisphere; n.d. , central 

 grey matter (nucleus dentatus) seen as a wavy 

 line ; s.m.v., superior (anterior) medullary 

 velum; Iny, lingula ; s.c.p., superior cerebellar 

 peduncle cut longitudinally ; cr., combined sec- 

 tion of the three cerebellar peduncles (the limits 

 of each are not marked) ; c.q.s. , c.q.i., corpora 

 quadrigemina (superior and inferior) ; fr, frsenu- 

 lum veil ; /, fibres of the fillet, seen on the sur- 

 face of the tegmentum ; c, crusta ; l.g., lateral 

 groove ; c.g.i., corpus geniculatum internum ; th, 

 posterior part of thalamus ; p, pineal body. The 

 Roman numbers indicate tho corresponding cra- 

 nial nerves. 



into which a pointed tent-shaped pro- 

 jection of the roof of the ventricle extends ( fig. 59, A, in longitudinal section). 

 This projection is bounded below by the inferior medullary velum, which in like 

 manner is prolonged from the white substance of the central part of the cere- 

 bellum. It is less easily displayed than the superior velum, being concealed by 



Fig. 40. ANTERIOR BOUNDARY (FLOOR) OF THE FOURTH VENTRICLE. (E.A.S.) 

 NATURAL SIZE. 



m. s., median sulcus ; str, striae acusticaa, marking the limit between the pon- 

 tine part of the ventricle and the medullary part or calamus scriptorius; l.r., lateral 

 recess ; i.f., inferior (posterior) fovea ; a.c., ala cinerea ; t.a., trigonum acustici ; 

 s.f., superior (anterior) fovea, close to the lateral margin of the superior part of 

 the ventricle. 



ta a part of the cerebellum, which is attached to its under or 

 posterior surface. It will be further noticed in the description of 

 the cerebellum. BeloAV the inferior velum the roof is formed 

 by a simple layer of flattened epithelium covered by pia mater ; 

 but it is not quite complete, for there is a hole in it termed 

 the foramen of Majendie a little above the place where the central canal opens 

 out into the ventricle, and there are tA\ r o other apertures in the epithelial roof 

 in the lateral recesses just mentioned. At the sides and beloAV, this layer 

 of epithelium passes into continuity with the epithelium covering the floor, 



