94 PROFESSOR J. C. EWART AND MR J. C. MITCHELL ON THE 



the branchial region ; throughout the remainder of the inner loop, and the entire length 

 of the outer loop up to where it approaches the beginning of the canal, the same diameter 

 (about 2 mm.) is maintained. The part which runs forwards side by side with the first 

 part of the hyomandibular and the outer part of the infra-orbital has a diameter of 3'2 

 mm. The part in front of the gill region, like the part of the infra-orbital with which it 

 is continuous, lies in gelatinous connective tissue, some 3 mm. beneath the surface ; the 

 rest of the ventral loop occupies a very superficial position. There are extremely few 

 tubules given off from the ventral loop. Between the junction with the infra-orbital 

 and the gill region there are ten tubules (t.-t. n , fig. 7). Of these, the four anterior are 

 very short and near each other, while the remaining six are from 1*7 to 5 mm. in length, 

 and wider apart. From the outer limb of the ventral loop, only four tubules (t.-t. 15 , fig. 7) 

 arise : these tubules are wide apart, and they vary considerably in length and position, as 

 shown in figure 7. 



The dorsal extension of the hyomandibular canal is at first somewhat dilated, and at 

 some distance (about 3*5 mm.) from the surface; the remainder, which is flattened and 

 has a small lumen, occupies a superficial position, and takes an irregular course towards 

 the outer angle of the pectoral fin before it bends inwards to join the scapular branch of 

 the lateral canal. The expanded anterior portion does not open directly to the exterior, 

 but it has two tubules from the infra-orbital opening into its wide inner end, and two 

 infra-orbital tubules open into the canal as it leaves the dilatation. From the long part 

 of the canal that runs backwards over the ampullary canals to eventually end in the 

 offshoot from the lateral canal, thirty-nine tubules (t.-t. 5i , fig. 6) were given off in the 

 specimen figured. These, as the drawing indicates, are relatively numerous, and of 

 varying lengths. They all run outwards, the majority outwards and backwards. 



The two mandibular portions of the hyomandibular canals form a single canal behind 

 the mouth. They lie immediately beneath the thin skin covering the mandible ; and 

 they together give off twenty-six short tubules (t.-t. m , fig. 7) which open by a row of 

 minute pores posterior to the openings of the mandibular ampullary canals. 



Innervation. — The entire length of the hyomandibular canal (including the ventral 

 loop, the long dorsal extension, and the mandibular part) is innervated by the hyo- 

 mandibular branch of the facial nerve. This large nerve {Jim., fig. 6), as it approaches the 

 hyoid group of ampulla? (H.A., fig. 6), breaks up into numerous branches, the majority of 

 which terminate in the ampullae. Some of the branches for the sensory canal leave the 

 nerve before it enters the ampullary capsule, while others pass through between the 

 ampullae, and then radiate to the dorsal and ventral portions of the canal. 



The part of the canal in front of the hyoid group of ampullae is almost entirely 

 supplied by branches which leave the nerve before it enters the ampullary capsule. 

 From these branches nine nerves were given off to the anterior part of the hyomandibular 

 canal (fig. 7). The whole of the long ventral loop, with the exception of the curve formed 

 by the outer limb and the straight part that lies alongside the infra-orbital canal, is 

 supplied by branches of the hyomandibular nerve, which penetrate the ampullary capsule 



