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Transverse Fibers of Pons

pontis, pars, nucleus, basilar and superficial

TRANSVERSE FIBERS OF PONS The transverse fibers form two consecutive layers in the pons, viz., the basilar, and the dorsal layers. They lie one upon another. The former are situated in the basilar part of the pons, the latter in the dorsal part (Figs. 113-118).

Basilar Fibers.—The superficial transverse fibers are an terior in position and form a thin compact layer constituting the anterior surface of the pons (Fig. 113). They are not inter sected by longitudinal fibers; but, otherwise, are like the deeper transverse fibers of the pars basilaris pontis.

Deep Transverse Fibers of Pars Basilaris.—These form a . thick lamina posterior to the superficial transverse fibers and in contact with the superficial lamina. They are intermingled with longitudinal fibers from the bases pedunculi, viz., the pyramidal, fronto-pontal, temporo-pontal and intermediate tracts (Figs. 113-118). In the meshes between the inter secting fibers is a large mass of gray matter on either side called the nucleus pontis. The deep and superficial transverse fibers of the pars basilaris pontis form the brachia pontis cerebelli. Their origin is found in the opposite nucleus pontis and nucleus ponto-bulbaris. They continue the indirect efferent path from the termination of the fronto-pontal, temporo-pontal and inter mediate tracts in the nuclei pontis and ponto-bulbaris to the cerebellar cortex of the opposite side.

In connection with the superficial and deep transverse fibers in the basilar part of the pons there should be mentioned an independent strand, the fila lateralia pontis, which is situated at the upper border of the pons and buried more or less in the isthmian furrow between the pons and mid-brain. It is called

by Henle the tmnia pontis. According to Sir Victor Horsley it rises from the nucleus pontis just ventral to the interpeduncular ganglion and, winding round the isthmus, enters the cere bellum through the brachium conjunctivum. Its destination is probably the nucleus dentatus and nucleus fastigii (Brain, Vol. 29, No. 113).

Dorsal transverse fibers of the pars dorsalis pontis (Fig. 114) compose a thin layer on the dorsum of the basilar transverse fibers; they belong to the formatio reticularis. This transverse lamina is present only in the inferior part of the pons. It is called the corpus trapezoideum. Its fibers inter sect those of the medial fillet.

The trapezoid body (corpus trapezoideum) lies in the dorsal part of the pons, next the boundary between the pars basilaris and the pars dorsalis pontis. Its fibers rise chiefly from the ventral nuclei of the cochlear nerve and, after decussating in the raphe, are continued up in the lateral fillets to the inferior quadrigeminal colliculi and brachia. A few fibers join the tract directly from the cochlear nerve. The nuclei of the trapezoid body, of the superior olive, etc. (olivary group), form relays for a number of its fibers. The corpus trapezoideum with the medullary strim and the lateral fillet which is the continuation of both, form the second stage in the auditory conduction path; and the auditory impulses are continued (a) through the brachium quadrigeminum inferius and (b) the acustic radiation to the temporal cortex (Figs. 116, 118 and 119).