POXS VAROLII. 511 



to the outside and in front of the vagal nucleus, which gives origin to 

 the fibres of the glosso-pharyngeal nerve. The post-pyramidal and 

 restiform ganglia have by this time become blended, and constitute 

 the lower part of the inner nucleus of the auditory nerve (fig, 357, 

 F viii'). 



At the point of the calamus scriptorius the prominence on each side 

 of the median furrow indicates the position of the lower part of the 

 vagal nucleus. A little higher up these vagal eminences diverge, and 

 between them the hypoglossal nuclei come to the surface. A depression 

 on each side of the vagal eminence separates it from that of the inner au- 

 ditory nucleus. Beneath this groove, just below the stri« meduUares, lies 

 the nucleus of the glosso-pharyngeal nerve. The hypoglossal nuclei cease 

 near the stria3 medullares, but the eminence beneath which they lie 

 blends with that of the vagal nucleus and is continued upwards as the 

 " eminentia teres." Beneath it, above the stride medullares, lies the 

 common nucleus of the sixth and facial nerves. (See p. 513. _) 



THE PONS VAROLII. 



The pons Varolii or tuher annulare (mesocephalon of Chaussier), 

 forms an eminence of transverse fibres above and in front of the medulla 

 oblongata, below and behind the crura cerebri, and between the lateral 

 hemispheres of the cerebellum. (Fig. 361.) Its margins are arched ; 

 the superior much more so than the inferior, and at the sides its trans- 

 verse fibres are much more gathered together, forming, at the place 

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

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

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

 small branches of the artery. 



The superficial fibres are transverse in their general direction, but 

 while the middle fibres pass directly across, the lower set ascend slightly, 

 and the superior fibres, which are the most curved, descend obliquely 

 to reach the crus cerebelli on each side ; and some of the latter cross 

 obliquely the middle and lower fibres, so as to conceal them at the 

 sides. 



Internal Structure. — The pons consists of the longitudinal or 

 peduncular fibres prolonged upwards from the medulla oblongata, of 

 its own transverse or commissural fibres, through which the lougitu 

 dinal fibres pass, and of a large intermixture of grey matter. When 

 the superficial transverse fibres are removed, the prolonged fibres of the 

 anterior pyramids come into view ; these, as they ascend through the 

 pons, are separated into smaller bundles, intersected by other trans- 

 verse white fibres, which, with those upon the surface, are all continued 

 into the middle peduncle of the cerebellum (see fig. 358). 



Opposite the lower part of the pons, behind the fibres from the ante- 

 rior pyramids, is another set of transverse fibres, which have a very 

 uniform course (fig. 359, t ). They constitute the trapezium, so called 

 because in most of the lower animals, in which the lower fibres of the 

 pons are not developed and the anterior pyramids are small, these 

 transverse fibres partially appear on the surface in an area of a some- 

 what four-sided shape. Externally they curve round, and many are con- 

 nected with, a collection of grey matter above them, called the superior 

 olivary body, and then course outwards, across the fibres of the facial 



