Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 293 



ersed the third segment and then the second septum, and entered 

 the second segment. 



The most posterior of the two horizontal branches ran outward 

 in the fourth muscle segment, to which it had the relations of 

 the corresponding branches of the spinal nerves in the posterior 

 muscles segments. The other, or anterior horizontal branch, ran 

 forward and outward, traversed the third and second septa and 

 the intervening third muscle segment, and then ran outward in 

 the second segment, as its horizontal nerve. As it traversed the 

 third segment it sent a horizontal branch outward in that segment. 



The three ventral branches ran downward, relatively close to- 

 gether, along the lateral surface of the skull, and passing anterior 

 to the ligamentum occipito-supraclavicular reached the inner sur- 

 face of the trunk muscles. The two posterior branches here lie 

 close together, the anterior branch issuing from the muscle mass 

 slightly in front of them. Running downward and backward, 

 the first and second nerves first unite, and then the nerve so 

 formed unites with the third nerve, a single trunk thus being 

 formed. From this trunk, or even from the first two nerves 

 before they have been joined by the third one, a branch is sent 

 downward and forward along the anterior edge of the mesial 

 surface of the clavicle, the remainder of the nerve running on- 

 ward toward the fin and becoming, after it has received a branch 

 from the first spinal nerve, the nervus pterygialis. The an- 

 terior branch runs internal to the pharyngo-claviculares, near 

 their origins from the clavicle, and enters the sterno-hyoideus. A 

 small branch is sent from this nerve to certain muscle fibers along 

 the inner surface of the clavicle that seem to belong to part of the 

 muscles of the ventral fin. 



The nervus pterygialis has the course already described in 

 describing the muscles of the pectoral fin. 



No branches of any of the nerves could be traced into the first 

 muscle segment of the trunk. 



There are thus in Scomber, if one considers only the foramina 

 of the nerves, three occipital nerves ; but as all the branches of 

 the posterior one of these three nerves innervate the fourth muscle 

 segment, and as that segment lies between the hind end of the 

 skull and the first free vertebra, the nerve that innervates it is, 



