548 THE NERVOUS SYSTEM 



ascending and descending branches in the usual manner, and most 

 if not all of them terminate in one of these two nuclei. A few 

 fibres, however, are undoubtedly continued past the cochlear nu- 

 clei without interruption. The ventral cochlear nucleus probably 

 receives the unusually short ascending branches, while most of the 

 descending branches end in the tuberculum acusticum, which is 

 continued spinalward for a considerable distance. 



From the ventral nucleus neurones of the second order send 

 their neuraxes in a ventro-mesial and somewhat cephalad direction 

 to collectively form the trapezoid body, a compact fibre bundle 

 which decussates behind the mesial fillet and enters the superior 

 olivary nucleus of the opposite side. This nucleus is closely ap- 

 plied to the dorsal surface of the trapezoid body. 



The neurones of the second order which arise in the dorsal 

 cochlear nucleus or tuberculum acusticum, reach the opposite su- 

 perior olive by a more circuitous route. They first pass dorsalward 

 to the lateral margin of the floor of the fourth ventricle ; in this 

 grey matter they turn toward the median line, forming superficial 

 coarse groups, the striae acusticce, which appear as macroscopic 

 transverse ridges in the ventricular floor. At the lateral margin 

 of the abducens these fibre bundles suddenly dip into the substance 

 of the pons, pass ventral to the nucleus of the sixth nerve, decus- 

 sate through the median raphe, and reach the opposite superior 

 olivary body in which most of these fibres terminate. 



Some fibres from the tuberculum acusticum and striae acus- 

 ticae, as also some from the mesial nucleus and trapezoid body, are 

 continued past the superior olives and enter the lateral fillet with- 

 out interruption. The lateral fillet, however, consists chiefly of 

 neurones of the third order, which arise in the superior olive of the 

 same side. This tract is continued cephalad, lying at first near the 

 lateral margin of the tegmental portion of the pons and dorso-lat- 

 eral from the mesial fillet. The lateral fillet soon blends with the 

 lateral margin of the mesial fillet to form a continuous sheet of 

 longitudinal fibres. In the mesencephalon some at least of the 

 neurones from the lateral fillet are interrupted at the inferior 

 corpora quadrigemina, their neuraxes terminating by arborization 

 about the scattered nerve cells of these bodies. From this point 

 the auditory path is continued cerebral ward by fibres which prob- 

 ably accompany the mesial fillet. 



The seventh or facial nerve (Figs. 385, 386, and 387). The 

 peripheral neurones of this nerve, which in man is a purely centri- 



