ORIGIN OF THE CEREBRAL NERVES. 505 



internal division of the cms cerebelli (fig. 257, vm, SFO). 

 These masses gradually and coincidently disappear below the 

 fasciculi passing into the librae arcuatse of the posterior area of 

 the medulla oblongata. 



Situated at first immediately by the side of the internal 

 auditory nucleus is a median elevation that Clarke has recently 

 correctly designated the fasciculus (eminentia) teres (fig. 257, 

 x 4 x) ; for the hypoglossal nuclei never extend as far as the 

 ependyma of the grey floor, but are covered both in the calamus 

 scriptorius, and in front of the central canal, by the eminentia 

 teres (fig. 258, where it appears in the form of a dark mass be- 

 hind XII 1 and xii 2 ), which is composed of small nerve corpuscles, 

 having a length of 21 30 ^, and a breadth of 6 9 p, and a 

 large number of fibres. The eminentia teres has a fusiform 

 appendage, the " median nucleus," on its inner side, and near 

 the middle line, composed of the same elements (figs. 257, x 3 ; 

 258, XI 3 ). Both of these clusters, which are to be regarded as 

 nuclei of origin of the lateral system, are thickest beneath the 

 strise, and becoming attenuated assume a club-shaped form 

 below. 



It is requisite to distinguish in transverse sections the ante- 

 rior angle of the grey floor from the auditory nucleus and the 

 eminentia teres ; for it is received between the diverging boun- 

 dary lines of these two masses, and higher up in the medulla 

 oblongata includes in its substance the two glosso-pharyngeal 

 nuclei of Clarke, which are inconsiderable clusters of nerve 

 corpuscles that are for the most part fusiform and have a length 

 of 45 /x, and a breadth of 15 /*. The external is situated in the 

 apex of the anterior angle, the internal about one millimeter 

 further inwards. 



At lower planes of section the anterior angle is occupied by 

 the posterior nucleus of the vagus (fig. 257, x 1 ), a mass in which 

 Clarke also distinguishes an internal and an external nucleus. 



This cluster of fusiform corpuscles, having a length of 30 

 45 ju, and a breadth of 12 15 p, extending towards the point 

 of emergence of the roots, is the upper part of the vago-acces- 

 sory nucleus of Stilling, and, with the glossopharyngeal nuclei 

 of Clarke, may be regarded as the posterior column of origin of 

 the mixed lateral system, the continuation of which in the 



