78 PROFESSOR J. C. EWART ON THE 



Leaving out of consideration the auditory nerve (Aw., fig. 2), the next dorsal branch 

 springs from the glossopharyngeus. This nerve I have traced to the skin over the 

 auditory region, but though I have not yet succeeded in tracing it to any of the sense 

 organs of sharks, I am inclined to believe that, as shown in the scheme (gl., fig. 2), it 

 innervates one or more of the sense organs immediately in front of the most anterior 

 organs supplied by the lateralis nerve, and also the auditory group of follicles (pit 

 organs) found in the skate. Allis has shown that it supplies one sense organ, and a 

 long transverse row of pit organs in Amia (gl., fig. 3). Hence its direct relation to sense 

 organs has been sufficiently established in at least one group of fishes. Pit, or at least 

 pit-like, organs are sometimes found in the mouth and pharynx of fishes, almost identical 

 with those in the skin. Sometimes they lie in the sides of the branchial clefts, and 

 they are even said to extend into the oesophagus. The pit-like organs in the mouth are 

 usually described as taste-buds. In the mammal they are said to be innervated by the 

 glossopharyngeal nerve, and it has been suggested by Beard and others that they are 

 modified lateral sense organs that have reached the back of the tongue, palate. &c. 

 through one or more branchial clefts. If the taste-buds are altered lateral sense organs 

 innervated by the glossopharyngeus, the fibres reaching them will belong to the dorsal 

 branch. It does not, however, follow that because the taste-buds are innervated by the 

 glossopharyngeal they are altered lateral sense organs, for the nerves reaching them may 

 spring from the pharyngeal branch, and consist of special sensory splanchnic fibres. 



The next dorsal branch (In., fig. 2) arises from the great vagus complex. It is not 

 yet possible to speak definitely as to the dorsal branches of the vagus for the reason that 

 it has not yet been determined how many of the branchial sense organs lying above the 

 branchial clefts of the vagus take part in the formation of the lateral canal. According to 

 Beard (27), " the ' lateral line ' has arisen solely by the extension and multiplication of 

 the primitive branchial sense organs of the vagus." He observes they are " connected in 

 development, being formed from one continuous sensory rudiment, and as they form one 

 physiological whole, we could expect a connection in the adult." Beard describes first 

 what he terms vagus I., i.e., the nerve of the first vagus cleft. It appears that from the 

 long sensory thickening above the vagus clefts, to which the broad band representing all 

 the vagus nerves grows out, there is soon slightly separated the anterior portion which 

 gives rise to the ganglion of vagus I., and later, to part of the supra-temporal branchial 

 sense organs. The rest of the sensory thickening is described as growing backwards along 

 the lateral surface of the trunk, i.e., the sensory cells, " which anteriorly give rise to the 

 compound vagus ganglion (v.g. 2, 3, and 4), repeatedly and rapidly divide," and thus 

 give rise to the "lateral line." Again, it is stated, "each of the elementary nerves 

 making up the vagus compound, viz., v.g. 2 and 3, and the intestinal branch, v.g. 4 and 5, 

 takes part in the formation of the so-called ' lateral line.' * In other words, " the lateral 

 line is made up of supra-branchial nerves of at least four segmental nerves, probably of 

 more than four, viz., vagus 2, 3, 4, and 5." It is further stated, that there is only one supra- 

 branchial branch — the lateral nerve — for all the elements of the vagus except the first (27). 



