MAMMALIAN. 5]^ 



entirely covered by a remarkable fringe of fibres emanating from the anterior border 

 of the auditory mass (Figs. 10% 11"), among which are finally developed the cells 

 of the fasciculus teres or common nucleus of the facial and abducens nerves. 



As the roots of the facial are more and more developed the whole auditory nucleus 

 is thrust outwards and backwards, changing form slightly, and sending out a process 

 or bundle of fibres into the caput cornu with which it becomes closely connected. 

 This gradual pushing outwards and backwards of the auditory nucleus, together 

 with the gradual lateral elongation of the whole medulla in this region, continues 

 as the facial makes its appearance, and the connection with the caput becomes more 

 and more intimate, until in the lower part of the pons Varolii the two form together 

 the great nucleus from which the trifacial nerve arises. 



As ah-eady pointed out by Clarke, the outer portion of the auditory nucleus 

 together with the restiform body, is thrown backward into the cerebellum, numerous 

 fibres from the main nucleus arching over the fourth ventricle, Avhilst others pass 

 backward into the cerebellum. 



The cells of the auditory nucleus present almost every variety in size and form, 

 some of them being exceedingly small, while, as already noticed by Schroder van 

 der Kolk, some are the largest anywhere found, even exceeding in size those of 

 the anterior cornua of the spinal cord. In the lower part of the medulla the cells 

 of the auditory nucleus are mostly smaU, oval or stellate, with every variety of 

 intervening form, measuring -^-^-^-^ to gi-g- of an inch in the sheep, and are inter- 

 spersed with scattered nuclei and granules with which the entire mass seems 

 filled, resembling those found in the posterior cornua of the spinal cord. Higher 

 up, the anterior part of the nucleus, especially that which represents the continuation 

 of the hypoglossal column, contains the same small cells and nuclei, but posteriorly, 

 near the entrance of the posterior division of the auditory nerve, the cells are at 

 first small, and oval, fusiform or crescentic in shape ; a little further inwards they 

 are quite large, some of them being very much elongated, oval, fusiform or semi- 

 lunar in shape, measuring in the sheep -^^-^ to 2-^0 ^^ ^^ vach. in length. In the 

 cat they are smaller, measuring -^\-^ to j\-^ of an inch. The lateral and postero- 

 lateral border of the main nucleus, together with its contiguous network, contains 

 very many large multipolar and stellate cells, sending out their processes in 

 every direction, especially among the longitudinal bundles which penetrate the 

 network and are inclosed in meshes of fibres formed chiefly from the interlacing 

 processes of these large cells. Some of the cell-processes pass inwards towards 

 the deeper lying portions of the nucleus or towards the cerebellum, while 

 others pass outwards among the longitudinal fasciculi towards the restiform 

 body, where they often form a very complicated system of radiating fibres, 

 connected with the root-bundles and with the longitudinal fibres of the resti- 

 form column. Some also pass longitudinally upwards or dovpnwards, and serve 

 to connect different planes of the medulla and trapezium. The cells situated 

 in the outer network of the auditory nucleus are the largest I have anywhere found, 

 measuring in the sheep from ^-J-g- to -^^-^ of an inch in diameter, in the cat from 

 ■5I2 to 2 6 6 of ^^^ inch. In the cat they are especially numerous, quite filling the 



