Xos. IAXD2.] AXATOMY OF SCOMBER SCOMBER. 223 



muscle segment thus here being' pinched off, no muscle fibers here 

 reaching to the mid-vertical plane of the body. Continuing its 

 course across this first posterior dorsal arch, the septum approaches 

 somewhat the line of the next or second posterior dorsal arch, but, 

 before reaching that arch, turns upward and backward approxi- 

 mately parallel to it and reaches the level of the line of the dorso- 

 posterior pockets. There it turns sharply forward and slightly 

 upward, crosses the lines produced of three or four dorsal verte- 

 bral arches, and, having reached the level of the dorso-anterior 

 pocket of the septum, turns sharply backward and continues in 

 that direction to the dorsal surface of the body. 



The first complete intermuscular septum, that is, the first one 

 that extends from the mid-dorsal to the mid-ventral line of the 

 body, is, as already stated in an earlier work (No. 6), the sixth. 

 The ventral part of the fifth septum, as seen on the inner surface 

 of the body wall, extends in a nearly straight line, from the ver- 

 tebrae to which it is attached, downward and backward until it 

 almost meets, at approximately a right angle, that part of the 

 sixth septum that lies distal to its ventro-posterior angle. There 

 it ends, so far as could be determined. The fifth septum thus does 

 not present a ventro-posterior angle, or its segment a correspond- 

 ing pocket. In the ventral half of this part of its length this sep- 

 tum follows the posterior portion of the ventral edge of the large, 

 posterior accessor}^ shoulder-girdle bone, the postero-ventral, spine- 

 like end of that bone lying in the inner edge of the septum. 



The mesial edge of the fourth septum extends downward and 

 backward from the vertebral column less than one half as far as 

 the fifth septum, its ventral end running onto the ventral edge of 

 the large, posterior accessory shoulder-girdle bone somewhat in 

 front of the point where the fifth septum reaches it. The third, 

 second and first septa all extend but a short distance below the 

 horizontal septum, their ventral portions forming, with that sep- 

 tum, small muscle pockets. 



The fifth septum in Scomber thus seems to mark the anterior 

 limit of the muscle segments that lie completely posterior to 

 the clavicle. According to Corning (No. 20) this septum marks, 

 in all teleosts, the posterior limit of the muscle segments that take 

 part in the formation of the "Hypoglossusmusculatur." It has 



