126 



single trunk. The ventral ends of the first and second efferent 

 arteries are connected by longitudinal commissure, as they are in 

 Gadus morrhua, a loop thus being formed around the ventral end of 

 the first gill cleft. Across the anterior end of this commissure, in 

 Gadus aeglefinus, the first efferent branchial artery is continued for- 

 ward and mesially and meets and anastomoses in the middle line 

 with its fellow of the opposite side, this cross-commissure not being 

 given, so far as I can find, in any of the descriptions of Gadus 

 morrhua. From the hind end of the longitudinal commissure a 

 branch is sent mesially and backward, and meeting its fellow of the 

 opposite side in the median line, ventral to the truncus arteriosus, 

 there gives origin to a median hypobranchial artery, as in Gadus 

 morrhua. 



Slightly dorsal to the point where the ventral longitudinal com- 

 missure, above described, joins the ventral end of the efferent artery 

 of the first branchial arch, a branch arises from the latter artery and, 

 running downward and forward, pierces the hypohyal and then, as 

 the afferent mandibular artery, turns upward along the antero-lateral 

 surface of the ceratohyal near its dorso- anterior (internal) edge. 

 Just before this afferent mandibular artery pierces the hypohyal it 

 sends a small branch upward in the hyoidean arch, along the 

 posterior surface of the ceratohyal, this branch being the afferent 

 hyoidean artery, and quite undoubtedly a secondary afferent artery, 

 as already fully explained in both Esox and Salmo. When the 

 afferent mandibular artery reaches the dorsal (proximal) end of the 

 ceratohyal it traverses the suspensorial apparatus, crosses the external 

 surface of the symplectic, retraverses the suspensorial apparatus, and 

 then runs upward internal to the hyomandibular to enter and supply 

 the pseudobranch, exactly as it does in Salmo. While this artery is 

 on the external surface of the suspensorial apparatus it sends one 

 branch backward to the opercular region and a second branch down- 

 ward and forward to the mandible; the mandibular branch being 

 a large one and separating into two branches one of which goes to 

 the external and the other to the internal surface of the mandible. 

 The afferent mandibular artery (so-called arteria hyoidea) of this fish 

 thus, as in both Esox and Salmo, does not traverse the hyomandibular 

 at any point. Just before it enters the pseudobranch it sends a small 

 branch upward to join the circulus cephalicus posterior to the point 

 of origin of the orbito-nasal artery ; this small branch, the homologies 



