Nos. IAXD2.] ANATOMY OF SCOMBER SCOMBER. 263 



tral edge turns sharply forward. In that position it continues 

 forward, lying dorsal to and close to the mandibularis externus 

 facialis. In some specimens the two nerves are easily separated 

 throughout their entire length : in others they were more or less 

 fused with each other. Toward the anterior end of the adductor 

 mandibulje muscle, the trigeminal branch turns downward and 

 then mesially, internal to the terminal branches of the facial nerve, 

 and reaching the ventral surface of the inferior division of the 

 geniohyoideus turns mesially and backward on that muscle (Figs. 

 56-57). Before leaving the mandible a branch is sent forward 

 into the dentary, which it pierces, and issues upon its external sur- 

 face. From this last branch two or more delicate branches are 

 sent to the tissues between the anterior ends of the mandibles, near 

 the symphysis, and possibly also to the degenerate intermandibu- 

 laris muscle, though this muscle seemed to receive branches from 

 the main inferior maxillary nerve, as will shortly be described. The 

 main branch, continuing mesially and backward on the ventral 

 surface of the geniohyoideus, soon reaches the mid-ventral line 

 of the head, where it joins and anastomoses completel\' with its 

 fellow of the opposite side of the head. Running backward a 

 short distance, in the mid-ventral line, the single nerve strand soon 

 separates into two parts, each of which runs backward and later- 

 ally, in a wavy course, on the ventral surface of the corresponding 

 geniohyoideus to the place where that muscle becomes entirely ten- 

 dinous. There the nerve penetrates the muscle, turns almost di- 

 rectly backward, approximately along the middle line of the ex- 

 ternal surface of the ceratohyal, and so continues until it reaches 

 the hind edge of the tendinous part of the geniohyoideus, where it 

 turns downward and backward and joins the ramus hyoideus faci- 

 alis between the fourth and fifth branchiostegal rays counting from 

 above downward. A part of this long hyoid part of the nerve, 

 starting from the mid-ventral trunk formed by the anastomosis 

 of the nerves of the two sides of the head, belongs, most certainly, 

 to the ramus hyoideus facialis, but how much of it belongs to that 

 nerve and how much to the trigeminus it is impossible to tell, there 

 being no interruption whatever in the course of the nerve. From 

 the fused nerves branches are sent to both divisions of the genio- 

 hvoideus. and, if Hcrrick is right in his work on Mcnidia (No. 38, 



