3g6 John F. Holm 



exists of its origin in the Medulla oblongata and subsequent course, 

 though in other fishes they have been investigated by a number of 

 anatomists. 



Sanders (41) describes the Trifacial nerve as arising by a 

 single root from the anterior end of the lateral tuberosities of the 

 Medulla oblongata and its fibres as passing backv^^ards in the same, 

 outside and above the Latero-ventral ganglion; the fibres could not 

 be traced into the lateral column of the spinal cord but disappeared 

 from view in close proximity to it. He could find no other root 

 and he considers this one corresponding to the ascending one in 

 higher vertebrates. 



Ahlborn (2), who has investigated the same matter in Petro- 

 myzon, finds one sensory root of the fifth nerve in the Medulla 

 oblongata and in the rostral part of Medulla spinalis. 



In the lateral part of the Funiculus dorsalis of the spinal cord 

 there may be seen one at first badly differentiated but afterwards 

 sharply defined fascicle, consisting of fine nerve fibres, which fascicle 

 continues up into the Medulla oblongata, getting gradually from a 

 dorsal into a more lateral position. This Ahlborn (2) describes as 

 the most important amongst the nerve nuclei and calls it the nucleus 

 of the ascending root of the fifth nerve. After its exit from the 

 brain it soon divides into two parts, the lateral and ventral fibres 

 entering the ventral part of the Ganglion gasseri; the rest runs 

 further forward and after penetrating the skull enters the dorsal part 

 of the same ganglion, which it leaves as the Ramus ophthalmicus 

 nervi quinti. The motor elements of the Trigeminus Ahlborn (2) 

 describes as situated in the Medulla oblongata and as springing 

 from one transverse and one descending root. The transverse root, 

 which is the most important, is found in a large-celled ganglion, but 

 the position of the descending root's nucleus Ahlborn (2) has not 

 been able to ascertain. 



A number of observations have been made as regards the origin 

 of the Trigeminus in the Elasmobranches and Teleostei. In the 

 older investigations, as, for instance, in those of Rohon (35) and 

 Fritsch (10), nothing very definite is said. Rohon (35) describes 

 an ascending root springing from the Funiculi dorsales, other fibres 

 being received from the Raphe and from the Lobus trigemiui. 



Stieda (44) describes the Trigeminus as having one posterior and 

 one anterior root nucleus, and Fritsch (10) finds the descending root 

 springing from large motor cells, the Trigeminus also receiving 



