462 THE NERVOUS SYSTEM. 
as they are traced to the surface and subdivide the substance of the medulla, as seen in transverse 
section, into the three areas of Flechsig, viz. an anterior, a lateral, and a posterior. 
The anterior area, which is bounded internally by the median:raphe and externally by the 
hypoglossal roots, presents within its limits: (a) the formatio alba; (6) the pyramid; (c) the 
fillet ; (d) the posterior longitudinal fasciculus ; (e) the mesial accessory olivary nucleus ; (f) the 
arcuate nucleus. 
The lateral area lies between the root fibres of the hypoglossal and those of the vagus. It 
contains: («) the inferior olivary nucleus ; (b) the dorsal accessory olivary nucleus ; (c) the nucleus 
lateralis; (d) the nucleus ambiguus, or the motor nucleus of the vagus and glosso- pharyngeal 
nerves ; (e) the formatio reticularis crisea. 
The posterior area is situated be hind the v agus roots, and within its limits are seen: (1) the 
restiform body ; (2) the upper part of the cuneate nucleus ; (3) to the inner side of this a crowd 
of transversely-cut bundles of fibres, loosely arranged and forming the descending root of the 
vestibular part of the auditory nerve ; (4) close to ‘these, but placed more deeply, a round, com- 
pact, and very conspicuous bundle of transversely-cut fibres, viz. the fasciculus solitarius, or 
descending root of the vagus and glosso-pharyngeal nerves ; (5) "the substantia gelatinosa Rolandi, 
much reduced, with the large spinal root of the trigeminal nerve close to its outer side. 
INTERNAL STRUCTURE OF THE PONS VAROLII. 
When transverse sections are made through the pons, it is seen to be composed 
of a ventral part and a dorsal or tegmental part. The ventral part is much the 
larger of the two, and, broadly speaking, it corresponds to the pyramidal portions 
of the medulla and the pedal portions of the two crura cerebri, which lie above it and 
appear to issue from it. The dorsal tegmental part may be regarded as the con- 
tinuation upwards of the formatio reticularis grisea and the formatio reticularis 
alba. As these parts are traced upwards into the pons they become much modified, 
and new constituents are added. 
Ventral Part of the Pons (pars basilaris pontis)—This constitutes the chief 
bulk of the pons. It is composed of: (1) transverse fibres arranged in coarse 
bundles; (2) longitudinal fibres, gathered together in massive bundles; and (3) a 
large amount of gray matter, termed the nucleus pontis, which fills up the inter- 
stices between the intersecting bundles of fibres. 
The longitudinal fibres, to a large extent, consist of the same fibres which, lower 
down, are gathered together in the two solid pyramidal tracts of the medulla. 
When the pyramids are traced upwards they are seen to enter the pons in the 
form of two compact bundles. Soon, however, they become broken up into 
smaller bundles by the transverse fibres of the pons, and are spread out over a 
wider area. At the upper border of the pons they again come together and form 
two solid strands, each of which is carried into the central part of the correspond- 
ing pedal portion of the crus cerebri. 
The transverse fibres at the lower border of the pons are placed on the super- 
ficial or ventral aspect of the pyramidal bundles. As we proceed upwards they 
increase In number, and many are seen breaking through the pyramids and even 
passing across upon the dorsal aspect of the latter. Laterally these transverse 
fibres are collected together into one compact mass, which enters the white central 
core of the cerebellum and constitutes the middle cerebellar peduncle. At the 
mesial plane the transverse fibres of the two sides of the ventral portion of the 
pons intercross and form a coarse decussation. 
The gray matter (the nucleus pontis) forms a considerable part of the bulk of 
the ventral portion of the pons. It is packed into the intervals between the inter- 
secting transverse and longitudinal bundles. 
There is a close analogy between the pyramidal portions of the medulla and the ventral 
part of the pons. In the medulla fine arcuate fibres on their way to the surface pass through 
the pyramids. Other superficial arcuate fibres sweep over the surface of the pyramids. These 
present a strong resemblance to the transverse fibres of the pons. They likewise reach 
the cerebellum, although by a different route, viz. the inferior cerebellar peduncle. The 
nucleus pontis is also represented in the pyramidal part of the medulla by the arcuate 
nuclei, which are covered over by the superficial arcuate fibres and even tend to penetrate, 
to a slight extent, into the pyramidal tracts. These arcuate nuclei, as already pointed out, 
are continuous with the nucleus pontis. 
Connexions of the Longitudinal and Transverse Fibres.—Our knowledge of 
the connexions of the longitudinal and transverse fibres of the ventral part of the pons is 
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