‘27 ve. Pa TS eT yg 
INTERNAL STRUCTURE OF THE PONS VAROLII. 465 
Upon the inner and dorsal aspect of the superior olive there is a dense group of longitudinal 
fibres. These constitute the central tegmental tract; but as precise information in regard to 
its connexions is still to a large extent wanting, it is not necessary to do more than indicate its 
position. 
(4) The posterior longitudinal bundle and the fillet come next. As they proceed 
upwards through the tegmental part of the pons, these longitudinal tracts occupy 
the same relative position as in the medulla. They are placed close to the median 
raphe; but they have drawn further apart from each other, and their fibres are 
more distinctly concentrated into separate strands, with an interval of some little 
width between them. The posterior longitudinal bundle lies immediately unde 
cover of the gray matter of the floor of the fourth ventricle. The fillet is placed 
close to the trapezial fibres, many of which traverse it as they pass towards the 
mesial plane. 
(5) The nucleus of the sixth nerve also forms a conspicuous object in sections 
through the lower part of the pons. It is a round mass of gray matter, which lies 
close to the outer side of the posterior longitudinal bundle, and immediately under 
cover of the gray matter of the floor of the fourth ventricle. From its inner 
side numerous root- bundles of the sixth nerve pass out and proceed forwards 
between the fillet and the superior olivary nucleus. They occupy in the pons, 
therefore, a position similar to that occupied by the hypoglossal root-fibres in the 
medulla. 
Up to the present only the lower part of the tegmental portion of the pons 
has been described, ¢.¢. the portion immediately adjoining the medulla. As we 
proceed upwards and gain a point above the level of the trapexial fibres, many of 
Superior medullary velum 
or valve of Vieussens 
Superior cerebellar peduncle 
: Floor of 
OR _— ventricle IV. 
Sa Posterior 
7 ongitudinal 
_-~ fasciculus 
Ay 7 
oe 
Motor nucleus of the fifth nerve 
Motor root of the fifth nerve— j ; ee reticularis 
Sensory nucleus of the fifth nerve 
Superior olive Corpus 
ei P 
trapezoides 
Sensory root of ; 
fifth nerve — 
Transverse 
~ fibres of pons 
Middle peduncle 
of cerebellum 
Pyramidal 
~ bundles 
Fic. 345.—TRANSVERSE SECTION THROUGH THE Pons VAROLII AT THE LEVEL OF THE NUCLEI OF 
THE TRIGEMINAL NERVE (Orang). 
the structures which have attracted attention lower down gradually disappear 
from the formatio reticularis. The posterior longitudinal bundle, the fillet, and 
the spinal root of the fifth nerve, however, are still carried upwards. Further, the 
30 
