50 ALLEN 



cavity a little to the right of the median line, the ventral artery 

 gives off numerous branches to the sternohyoideus muscle. In 

 the specimen from which fig. 12 was drawn, a vessel was 

 noticed branching off to the left, passing horizontally under 

 the ventricle, and terminating on the left precaval vein in the 

 neighborhood of the left subclavian sinus. Directly caudad of 

 this vessel and a little cephalad to the crossing of the sinus 

 venosus, the ventral artery sends off a pair of vessels to the 

 ventral muscles of the pectoral fin. Each of these hy^obranch- 

 ial arteries (PL II, figs. 12 and 14; Hypobr.A.) runs a short 

 distance caudad between the sternohyoideus and the pectoral 

 profundus adductor muscle, and then curves slightly dorsad, 

 passing between the inner surface of the coracoid and the pec- 

 toral profundus adductor muscle, giving off at least two branches 

 to the inner surface of the muscle ; then curving slightly ven- 

 trad, penetrates the basal canal of the pectoral rays,^ and 

 anastomoses in this canal with the internal subclavian artery 

 (2) (PI. II, fig. 14; I. Sub.A.(,)), but before entering this canal 

 the hypobranchial gives off a dorsal branch which passes be- 

 tween the pectoral profundus muscle and the brachial ossicles, 

 supplying the inner surface of the muscle. Continuing caudad, 

 the ventral artery passes under the sinus venosus between the 

 pelvic bones, giving off arteries to the body wall, the ventral 

 or pelvic fin muscles, and the ventral rays. The first con- 

 stant artery of any size to be given off from the ventral arter}' 

 after it reaches the ventral fin musculature is one which comes 

 out ventrad in a median line to the outer surface of the pro- 

 tractor muscle of the pelvic arch, where it divides at nearly 

 right angles, one branch supplying the left, the other the right 

 protractor muscle of the pelvic fins and the very large abductor 

 muscle of the ventral spine (fig. 12 ; Ab.V.S.). At various 

 intervals, usually alternating with the veins, the ventral inter- 

 costal arteries (^\. II, fig. 12 ; V.Intc.A.) are given off between 

 ever}' alternate pair of myotomes, and they anastomose with the 

 corresponding dorsal intercostal arteries. The ventral artery 



•Each pectoral fin ray consists of 2 separate halves, which are concave inside 

 and convex outside, and where their bases overlap the brachial ossicles in their 

 attachment to the shouldcr-t,nrdlc, there is formed a rather large canal at the 

 base of the pectoral fin. 



