138 THE SALAMANDER 



(iii) The trochlearis normally divides into two distinct rami, one 

 of which anastomoses with the Vth nerve while the other does 

 not. 



Before the significance of these facts can be adequately appreciated 

 a complete reinvestigation of the internal origin and development of 

 this nerve would be necessary. 



VI. N. Abducens (n.6) (somatic motor). This is one of the finest 

 of all the cranial nerves and one of the most difficult to investigate. 

 It arises by two roots from the ventral surface of the medulla very 

 far back — in fact posterior to the origin of the IX-X complex — 

 close to the mid-ventral line, and passes anteriorly and laterally 

 alongside the internal carotid artery, leaving the cranial cavity by a 

 special foramen — For. abducentis — just a little antero-mesial to the 

 palatine nerve. It enters the orbit mesial to the M. retractor bulbi. 

 In the adult Salamander the N. abducens is always quite distinct 

 throughout the whole of its course from the trigeminus, and from 

 the Gasserian ganglion, although, according to Hoffmann, it 

 approaches the latter fairly closely in the larva, while in some Uro- 

 deles, e.g. Triton, it actually enters the ganglion and leaves it in 

 company with true trigeminus fibres. It supplies the MM. retractor 

 bulbi and rectus posterior, and in order to reach the latter muscle 

 the nerve frequently bifurcates and passes round either side of the 

 M. retractor bulbi, supplying it with numerous fibres on the way, 

 or it may remain entire and pass round the lateral aspect of the 

 retractor muscle. 



So far as the present investigation goes, the MM. retractor bulbi 

 and rectus posterior of the Salamander are only supplied by the 

 abducent nerve which is distributed to these muscles alone. 



V. N. Trigeminus (n.5). The Vth nerve of the Salamander is 

 probably the most complicated of the cranial nerves. It possesses 

 the typical three branches which, however, are not quite typical in 

 composition, as will be seen later. The nerve arises from the 

 antero-lateral angle of the medulla, and passes immediately into 

 the. foramen ■pro-oticum situated just in front of the auditory capsule 

 which is formed by the junction of the trabeculae with the roof 

 of the ear capsules. Within this foramen lies the large Gasserian 

 ganglion from which the branches of the trigeminus nerve arise. 



Von Plessen and Rabinowicz describe two ganglia in connexion 

 with the Vth nerve; (i) an accessory (Neben-) ganglion associated 

 with a dorsal root, and (ii) a main (Haupt-) ganglion with a ventral 

 root. Now their 'Nebenganglion' is really the ganglion belonging 



