64 ALLEN 



spine ; and in the specimen from which fig. 16 was drawn, the 

 levator muscle of the second dorsal spine, as well as sending up 

 a branch behind the first dorsal spine. 



After giving off the first neural artery the subclavian might 

 be designated as the brachial artery as in mammals, but it 

 seems hardly advisable to press such homologies. Emerging 

 from the head kidney the subclavian passes ventrad along the 

 inner anterior surface of the pectoral superficial adductor mus- 

 cle ; and when the pectoral profundus adductor muscle is 

 reached, a branch is given off to the superficial muscle ; then 

 bifurcating, forms what I have designated as the external and 

 internal subclavians.^ The internal subclavian artery (PI. II, 

 fig. 14; I. Sub. A.) for a short distance continues along the 

 inner cephalic edge of the superficial adductor muscle ; then 

 divides into a sii^e7'jicial internal subclavian artery (PI. II, fig. 

 14; I. Sub. A. (1,), which after giving off a few branches to the 

 superficial adductor muscle continues obliquely ventrad along 

 the inner surface of the profundus adductor muscle ; and a ■pro- 

 fundus internal subclavian artery (PL II, fig. 14; I. Sub. A. (2,), 

 which immediately penetrates both superficial and profundus 

 adductor muscles and runs obliquely ventrad between the pro- 

 fundus muscle and the scapula, giving off several branches to 

 the former. In the neighborhood of the most dorsal pectoral 

 ray this vessel divides into a brachial ossicle artery and a pec- 

 toral fin artery. The brachial ossicle artery crosses these bones 

 in its ventral course just back of the pectoral rays, and ex- 

 hausts itself by giving off vessels to the distal part of the pro- 

 fundus muscle and by sending off branches between the ossi- 

 cles to the profundus muscle on the outside of the shoulder- 

 girdle. While the pectoral fin artery penetrates the basal canal 

 (see note, page 50) between the first, or most dorsal, and the 

 second rays, and continuing ventrad in this canal anastomoses 

 with the hypobranchial artery. Throughout its entire course 

 it gives off a branch to the central canal of each ray, which 

 soon divides, one branch continuing along the dorsal side of the 

 cavity and the other along the ventral side. The external sub- 

 clavian arte?y (P\. II, fig. 14; E. Sub. A.) immediately passes 



'Perhaps external and internal pectoral arteries would be better names. 



