272 THE RHOMBENCEPHALON. 



transverse lamina is present only in the inferior part of the pons. 

 It is called the corpus trapezoideum. 



The trapezoid body (corpus trapezoideum) lies in the dorsal 

 area of the pons, next the boundary between the pars basilaris 

 and the pars dorsalis pontis. Its fibers rise chiefly from the 

 nuclei of the cochlear nerve and, after decussating in the raphe, 

 are continued up in the lateral fillet to the inferior quadrigeminal 

 colliculus. A few fibers join the tract directly from the cochlear 

 nerve. The nuclei of the trapezoid body and of the superior olive 

 form relays for a number of its fibers. The corpus trapezoideum 

 with the medullary striae, and the lateral fillet, which is the con- 

 tinuation 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 temporo-thalamic 

 radiation to the temporal cortex (Fig. 89). 



LONGITUDINAL FIBERS OF PONS. 



The longitudinal fibers of the pons are arranged in two distinct 

 groups, viz., the ventral or anterior and the dorsal or posterior 

 (Figs. 87 and 88). The groups are separated by the trapezoid 

 body. 



The ventral longitudinal fibers are situated in the pars bas- 

 ilaris pontis (Figs. 87 and 88). Four fasciculi make them up. 

 They are the four motor tracts of the basis pedunculi. The fronto- 

 pontal, temporo-pontal and intermediate tracts terminate in the 

 nucleus pontis. The pyramidal fibers run from the middle three- 

 fifths of each basis pedunculi down through the middle trans- 

 verse layer of the pons to the pyramids of the medulla oblon- 

 gata. Together with the above cerebro-pontal tracts they form 

 a thick bundle on either side of the median line, which presses 

 down the superficial transverse fibers and produces the sulcus 

 basilaris. The nucleus pontis, one on either side, is situated among 

 the pyramidal fibers. The pyramidal tracts diminish in size dur- 

 ing their descent, because of the fibers which leave them to de- 

 cussate and end in the nuclei of motor cerebral nerves. 



The Dorsal Longitudinal Fibers. These are contained in 



