154 Cincinnati Society of Natural History. 



nuclei, which are the most obvious cell-clusters of the medulla. 

 These lie in the eminentia acustica, or great dorsal and median 

 projections of the walls of the fourth ventricle. The main nucleus 

 is in the caudad or lower division, which contains a very large 

 aggregate of flask-cells. The nucleus is more or less concavo-con- 

 vex or lenticular, and lies next the ventricle. The apex-processes 

 of the cells are connected with fibres passing medianly to the raphe, 

 from which point their distribution can not certainly be traced. 

 The blunt peripheral portion is connected by afferent fibres, with 

 the roots of (probably the cochlear branch of) the auditory nerve. 

 The second nucleus lies peripherad to the first as well as cephalad, 

 and is composed of two or more strata of more elongate fusiform 

 and larger cells imbedded in a compact gray gelatinous mass. The 

 course of the fibres centrally is the same as in the other nucleus, 

 while peripherally they may enter the branch to the labyrinth. 

 (Plate XV., Fig. 2.) The fact that the apical process is central in 

 these and other sensory cells, and peripheral in motor root cells, is 

 adverted to beyond. 



(9, 10.) The ninth and tenth nerves may be considered together. 

 Their nuclei are closely associated upon the upper lateral portion 

 of the clava. The glosso-pharyngeal springs from a point a little dor- 

 sad and cephalad to the others, and consists of a single clustre of 

 fibres, which pass medianly to the gray matter about the ventricle 

 cephalad to the nucleus of the tenth. The ninth nerve may be in 

 this case purely motor at its origin. 



The tenth nerve, with its numerous roots, forms a continuous 

 series nearly the entire remaining length of the medulla, except for 

 a considerable hiatus separating the last cluster of two roots from 

 the anterior fibres of the tenth. It may be suggested that the 

 above-mentioned separate fibres are possibly the homologue of the 

 sensory roots of the twelfth nerve. The fact that the nucleus lies 

 dorsad to that of the twelfth in the same frontal plane, and that is 

 at least chiefly sensory, while the latter is certainly motor, is a curi- 

 ous coincidence when taken in connection with the apparent sup- 

 pression of the dorsal roots of the first cervical nerve. The nucleus 

 of the tenth is elongate, lying above the canalis centralis, and near 

 the median line. The cells are less than half the size of those of the 

 twelfth, and are largely flask-cells with the apex median, and giv- 

 ing off direct fibres, which leaving the blunt extremity ascend, and 

 then pass transversely to the roots. In some parts there seems to 

 be a mixture of pyramid and flask cells. (Plate XIII.) 



