loS ZOOTOMY. 



97. The body muscles (Fig. 30), distinctly divided into 

 vertical segments or myotomes, separated from one 

 another by septa of connective tissue : each myotome takes 

 a zigzag course, passing, from the middle dorsal line, at first 

 sharply backwards, then gently forwards, then gently back- 

 wards, and finally sharply forwards to the middle ventral 

 line. The myotomes are also more or less distinctly 

 divided into dorsal and ventral portions : the dorsal 

 muscles on nearing the head, turn forwards, and are inserted 

 into the frontals ; the ventral muscles being inserted into 

 the clavicles. 



98. The cutaneus quinti ( T), or cutaneous branch of the tri- 

 geminal nerve ( 193), seen emerging from between the muscles on 

 the dorsal surface of the head, and passing backwards and slightly out- 

 wards immediately beneath the skin. Soon after its origin it gives off 

 two or three small nerves which pass backwards and upwards, and, 

 uniting with one another form a trunk ( V] which runs along the bases 

 of the dorsal fins, as far as to the caudal. The main trunk of 

 the cutaneus quinti divides into two branches, one of which ( V") 

 passes downwards and backwards to the anal fins, supplying them in 

 the same way as the dorsal branch supplies the dorsal fins : the other 

 (V'"} passes along the outer face of the clavicle and sends branches to 

 the pectoral and pelvic fins. Traced forwards, the cutaneus quinti is seen 

 to make its exit from the skull by a foramen in the parietal ( 31). 



99. The cutaneus vagi, or cutaneous branch of the pneumogas- 

 tric nerve ( 196), emerging from beneath the operculum near its dorsal 

 end, having already divided into two trunks, which pass almost directly 

 backwards, the first {X} immediately beneath the skin of the lateral 

 line, the other (A") along the line of junction of the dorsal and ventral 

 muscles ; at about the level of the second dorsal fin these nerves begin 

 gradually to approach one another, and 1 he upper one soon fades off, the 

 lower one then passing along the lateral line to the tail. The two 

 trunks are united by one or two commissures. 



XVIII. Keeping the fish with its left side uppermost, 

 make a median ventral incision from the hip- 

 girdle backwards to within a quarter of an inch of 



