370 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



an independent branch arises for the oblique dorsal musculature of 

 the gill arches, which is, however, in part supplied by a branch of 

 tr. branch. IV. 



Directly behind the most posterior of the levatores branchiarum, 

 and separated by it from the nerves in front, the ramus lateralis 

 vagi originates from its subdivision of the ganglionic complex. It is 

 at first parallel in its direction to the transverse portion of the 

 supraclavicle, but afterwards crosses it (Fig. 14, PI. IV.) and becomes 

 superficial over the air-bladder and behind the ascending process of 

 the supraclavicle. Here it gives off its branch in the course of the 

 accessory lateral line which can be traced along the line of junction 

 of the ventral and lateral musculature as far as the line of attach- 

 ment of the superficial muscles of the anal fin (Fig. 6, PI. I.), while 

 the stem is continued backwards in the line between the dorsal and 

 ventral parts of the lateral musculature. Whether as Mayser asserts 

 for Cyprinus the fibres of the ramus lateralis are those which I have 

 named radix acusticus vagi I., I have been unable to demonstrate in 

 Amiurus, but the fact that the mucous canals of the head are sup- 

 plied by fibres from the ttiberculum acusticum would lead one to con- 

 clude that the same is true of those of the trunk. 



SPINAL NERVES. 



Of these there are forty-one pairs, of which the first emerge 

 through the exoccipitals, the more anterior of those which follow 

 by separate apertures for the dorsal and ventral roots through the 

 arches of the corresponding vertebrae (e. g., the 7th pair through the 

 arch of the 6th vei'tebra) and the more posterior through notches on 

 the posterior borders of the arches, which are closed into foramina by 

 articulating processes from the succeeding vertebra?. 



The second and third spinal nerves have no foramina, for owing to 

 the modification of the anterior vertebra? in connection with the 

 auditory organ, the wall of the neural canal is membranous in that 

 region. The dorsal and ventral root of the second are further apart 

 from each other than those of the third, but they emerge very close 

 to these, much closer than their points of origin from the spinal cord 

 would indicate. (Fig. 8, PI. IV., and Figs. 2 and 3, PL VI.) This 

 backward position of the points of emergence of the roots of the 

 second nerve is to be explained by the formation of that diverticulum 

 of the dura mater known as the atrium sinus imparls and the alteration 



