TEE PONS VAROLII. 521 



for the glosso-pharyngeal nerve is really the place of origin of the greater root of the 

 fifth or trigeminal nerve. 



Fig. 353. TRANSVERSE SECTION Fig. 353. 



OF THE MEDULLA OBLONGATA 

 (after Stilling). 



The section is made at the level 

 of the middle of the olivary bodies]; 

 the effect produced by transmitted 

 light is brought out on the left- 

 hand side of the figure, the half 

 to the right being only sketched, 

 a, anterior, and p, posterior 

 fissure ; b, anterior pyramid ; c, 

 olivary body with its corpus 

 dentatum shown internally ; d, 

 grey tubercle of Rolando in the 

 lateral column ; e, the restiform 

 body and its nucleus ; /, nucleus 

 of the roots of the glosso-pharyn- 

 geal nerve ; g, nucleus of the pneumo-gastric nerve ; h, that of the hypoglossal nerve ; 

 z, the septum or raphe ; 8, roots of the pneumo-gastric nerve emerging ; 9, roots of the 

 hypoglossal nerve. 



THE PONS VAROLII AND CEREBELLUM. 



THE PONS VAROLII or tuber annulare (mesocephalon of Chaussier, nodus 

 encepliali of B-au and Sommerring), forms an eminence of transverse fibres 

 above and in front of the medulla oblongata, below and behind the crura 

 cerebri, and between the lateral lobes of the cerebellum. Its margins are 

 arched ; the superior much more so than the inferior : thus, at the sides its 

 transverse fibres are much more gathered together, and form at the place 

 where it passes into the cerebellum a narrower bundle, which is named the 

 middle cms of the cerebellum. In the middle line the pons presents a 

 shallow groove in which the basilar artery lies, and is perforated by small 

 branches of that artery. 



Although the superficial fibres are transverse in their general direction, 

 they are not all parallel to each other. The middle fibres pass directly 

 across, the lower set ascend slightly, whilst the superior fibres, which are the 

 most curved, descend obliquely to reach the crura cerebelli on each side ; 

 and there are also one or more superficial bands of the superior fibres 

 which cross obliquely downwards over the middle and lower fibres, and 

 completely conceal them at the sides. 



In its internal structure the pons consists of the longitudinal or peduncular 

 fibres prolonged upwards from the medulla oblongata, of its own transverse 

 or conimissural fibres, through which the longitudinal fibres pass, and of a 

 large intermixture of grey matter. Behind the superficial transverse fibres 

 are seen the prolonged fibres of the anterior pyramids, which, as they ascend 

 through the pons, are widely separated into smaller bundles, intersected by 

 other transverse white fibres, which, with those upon the surface, are all 

 continued into the cerebellum. 



The alternation of transverse and longitudinal fibres just described extends 

 to a considerable depth in the pons, the quantity of transverse fibres greatly 

 preponderating ; posteriorly there succeeds a third layer, consisting entirely 

 of longitudinal fibres, and comprehending the olivary fasciculi, and the 

 fasciculi teretes. 



The median septum or raphe, which exists in the medulla oblongata, is 



M M 



