Kappers, Teleostean and Selachian Brain. 59 



increased in the oblongata by the addition of short association 

 tracts and they are distinguished from the dorsal fibers by their 

 more delicate medullary sheaths and by the fact that they do not 

 get their myelin as soon as the fasc. longitudinalis dorsalis, which, 

 moreover, is more heavily medullated. While the dorsalis fibers 

 have the appearance of primary and secondary motor fibers, the 

 thalamo-spinalis lacks these qualities. Since, however, the 

 fasciculus dorsalis is merely a collective name for different kinds 

 of fibers, there is no objection in principle to considering the other 

 longer and shorter association fibers as belonp;ino- to the fasc. dor- 

 salis. But even in this case I must deny that they form part of the 

 com. posterior or of the fibrae ansulatae thalami. 



As belonging to this tract I must mention also a connection with 

 the lateral part of the valvula cerebelli (not figured), which has 

 been mentioned also in Acipenser by Goronowitsch and John- 

 ston, in the region of the trochlears and oculomotorius nuclei. 

 I regard these fibers as a crossed connection between these nuclei 

 and the cerebellum, of which, however, I shall have more to say 

 in the fourth chapter. 



In the same place where these fibers leave the cerebellum another 

 tract enters the valvula directly mesad of those fasc. long, posterior 

 fibers. It is the tr. niesencephalo-cerehellaris superior (Figs. 

 xlvii to lii, Plate III, and Fig. 5, Plate XII), already referred to 

 when speaking of the com. horizontalis and the tr. rotundo- 

 lentiformis, with which it originates from the nucleus lentiformis 

 in the most anterior part of the eminentia medialis directly behind 

 the com. posterior. In Figs, xlvii and xlviii the fibers designated 

 as J7, ^2h, 25 contain the beginning of this tract which, continuing 

 its course in the same direction backward, runs mesad of the 

 colliculus and mesad of the colliculus-bundle, the fasciculus later- 

 alis, and directly adjacent to the latter, as Figs. 1 and li show. 

 But while the lateral fascicle runs backward into the oblongata, 

 the medial tract enters the valvula cerebelli and is still visible at 

 the base of the cerebellum in Fig. lii. In this region of the cere- 

 bellum, which must be regarded as the velum, the tr. mesenceph- 

 alo-cerebellaris superior runs through two roots of the nervus 

 trochlears which unite more laterally and then leave the velum 

 (Figs. Ixxxvi and Ixxxvii, Plate VI). 



This tract was first described by C. L. Herrick in his work on 

 the thalamencephalon and mesencephalon as arising in the region 



