50 GRAY SUBSTANCE OF THE TRAPEZIUM, 



CHAPTER II. 



THE AUDITOEY NUCLEUS AND ROOTS. 



The Nucleus. — In the preceding chapters on the morphological changes in the 

 medulla and trapezium, it has been shown that the auditory nucleus is developed, 

 as Clarke had already demonstrated,^ between the outer horn of the vagus nucleus 

 and the post-]3yramidal body, as a small triangular mass, apparently formed from 

 the substance of the two neighboring nuclei, with both of which it is very closely 

 connected. It sends out numerous fibres into the restiform body, which cross each 

 other at various angles, interlacing among and aroimd the numerous longitudinal 

 fasciculi which pass upwards along the outer border of the nucleus, thus forming 

 an open network which is very much developed in the upper parts of the medulla, 

 where it is closely connected Avith the remains of the restiform nucleus, forming 

 Avhat Clarke has called the outer portion of the auditory nucleus. 



The inner mass or principal nucleus of the auditory, enlarges tiU the nucleus of 

 the vagus is pushed quite forwards, the outer portion or network at the same time 

 increasing, tiU. it occupies a very considerable portion of the restiform column. 

 The next stage is that in which the auditory nucleus together with the glosso- 

 pharyngeal and hj^Doglossal nuclei, seem to be fused into one mass (Plates II and 

 XIV, Figs. 8, 8"), the glossopharyngeal distinguishable mainly by its more trans- 

 parent substance, appearing as a separate nucleus near the apex of the broad 

 triangular mass. From that portion of the triangle which is the continuation of the 

 nucleus of the hypoglossal, fibres run out in the direction formerly taken by the 

 hypoglossal roots (Fig. 8"), and form considerable bundles accompanied by cells 

 sometimes scattered and sometimes collected into groups, often quite filling the 

 antero-lateral portions of the medulla and apparently serving to connect the trans- 

 verse and arciform fibres with the neighboring parts. 



The large triangvilar nucleus is now filled with numerous cells, mostly of rather 

 smaU size, but larger near the apex and in the network or outer portion of the 

 nucleus. As we approach the trapezium, the outer network becomes more and 

 more developed, extending far out into the restiform column and containing 

 numerous very large cells (Figs. 9, 9"). Anteriorly or towards the raphe, the 

 remains of the hypoglossal nucleus become more and more separated from the mass 

 by the gradual pushing backwards of the auditory nucleus, its situation being almost 



' Philos. Trans. 1858. Proceedings of the Royal Society, 1861. 



