SENSORY CANALS OF L^MARGUS. 79 



From these statements I infer that while the supra-branchial branch of vagus I. (the 

 nerve of the first vagus cleft) supplies thesupra-temporal sense organs, the united supra- 

 branchial branches of vagus II. , III., IV., and V. form the lateralis nerve and innervate 

 the sense organs of the lateral canal of the trunk, or, more accurately, the sense organs of 

 the lateral canal not supplied by vagus I. 



In the case of the facial the majority of the sensory fibres for the sensory canals, 

 i.e., the fibres of which the superficial ophthalmic, buccal, and the greater part of the 

 hyomandibular nerves are largely composed, escape at a comparatively high level from 

 the side of the medulla. From the side of the medulla in front of and on a higher level 

 than the root of the glossopharyngeal and the rootlets which unite to form the chief 

 portion of the vagus, there escape a number of fibres which unite to form the nerve 

 (lateralis) which supplies the entire length of the lateral canal, the temporal commissure 

 included. In Lsemargus this nerve lies in intimate relation with the first division of 

 the vagus (vagus I.). In the skate, it is from the first a distinct nerve, with an inde- 

 pendent ganglion (l.g., fig. 2), but it may receive fibres from the branchial divisions of the 

 vagus. In Lsemargus the three posterior branchial divisions of the vagus, together with 

 the intestinal branch, are inseparably united, and in connection with one long ganglion, 

 but they send no distinct branches to the lateralis nerve. In Eaia, the three posterior 

 branchial branches of the vagus, and the intestinal branch, are in contact with each 

 other, but not blended, and each, like vagus I., has a distinct ganglion (I.-V., fig. 2), but, 

 as in Lsemargus, they send at the most very slender branches to the lateralis nerve. The 

 condition in the adult thus seems to indicate that the lateral canal as above described 

 has mainly arisen from the branchial sense organ above the first vagus cleft, and that the 

 epidermic thickenings above the second, third, and fourth vagus clefts, while probably 

 assisting in forming a long ganglion (Lsemargus), or four separate ganglia (Raia), have 

 taken little or no part in forming the "lateral line." The lateralis nerve behind the 

 first branchial cleft consists entirely of special sensory somatic fibres ; in front, it seems 

 to be accompanied by a few ordinary sensory fibres which reach the skin. 



If figure 2 is compared with the schemes previously published, it will be found to 

 differ in several important points. It contains not only the dorsal but also the more 

 important branchial and visceral branches, and in addition to the sensory canals, the 

 various groups of ampullae, and also the follicles or pit organs. 



It is not intended to represent the arrangement in any given Elasmobranch, but 

 rather to indicate the position, innervation, &c, of the lateral sense organs in a Selachian 

 having these structures well developed. In the schemes hitherto constructed, the relation 

 of the profundus nerve to the ciliary ganglion, and to the oculo-motor nerve, is not 

 shown, and it is taken for granted that the profundus supplies a group of sense organs. 

 This scheme represents (1) the dorsal branch of the profundus (o.n.) proceeding to the tip 

 of the snout without supplying either sensory or ampullary canals ; (2) the long ciliary 

 nerves (I.e.) passing to the eyeball ; and (3) the offshoot (l.r.) to the ciliary ganglion (e.g.); 

 this offshoot may, perhaps, be looked upon as a visceral branch. 



