365 



extent of this bundle (1, 1. c. ; 2, p. 365) and as the bundle passes 

 the chief motor nucleus of the trigeminus it sends a great number of 

 fine collaterals into that nucleus (4). On the whole these sound more 

 like the characteristics of a sensory bundle than of a motor. Indeed, 

 recent authors have avoided the assertion that this is a motor root 

 (see, for example, 2, pp. 91, 113, 365). The supposed nucleus of 

 origin in lower vertebrates has come to be known as the nucleus 

 magnocellularis tecti. 



The bundle in Teleosts was described by Mayser (13) and in Aci- 

 penser by Goronowitsch (14) as a bundle from the sensory root of 

 the trigeminus. Osborn (16) described the bundle in Cryptobranchus 

 as arising from the motor root, dividing into lateral and mesial bundles 

 opposite the cerebellum, and being distributed to nearly the whole wall 

 of the tectum. Edinger (2) speaks of the radix mesencephalica and 

 of its nucleus in reptiles and amphibia. Sargent (5) has described 

 the constituent fibers of the structure known as "Reissner's fiber" as 

 the neurites of the cells of the nucleus magnocellularis in several 

 vertebrates, and Houser (6) has confirmed this for Selachians. If this 

 is true it can scarcely be expected that a part of the same group of 

 cells would give rise to direct motor fibers of the trigeminus. 

 Kappers (7) denies the existence of a radix mesencephalica trigemiui 

 in either selachians or teleosts. Wallenberg (21) has described the 

 results of degeneration experiments on pigeons and ducks for the ex- 

 press purpose of tracing this tract. He finds descending degeneration 

 after injury to the optic lobes. The degenerating fibers seem to belong 

 to the motor root. 



While reviewing by means of Weigert preparations the account 

 of the cerebellum of Scyllium given by Edinger (3), the writer was 

 surprised to find that the course of this bundle was entirely clear 

 and that it conformed to the description of Mayser and Gorono- 

 witsch. Although the tract in question does not fall within the scope 

 of Edinger's paper he seems to have identified it with the tractus 

 cerebello-tectalis. His description of this tract is very unsatisfactory. 

 He states that it is doubtful whether the tract belongs to the cere- 

 bellum, that he considers it "durchaus möglich" that it arises from 

 the large cells which are usually homologized with the nucleus of origin 

 of the trigeminus root, and that the tract may be a dorsal root of 

 the trochlearis. He recognizes the radix mesencephalica trigemini 

 behind the cerebellum (Fig. 12 N.V. rad. mesenc), although in his 

 description and in Fig. 1 he assigns the fibers in the tectum to the 

 cerebellar tract. 



