180 JEREMIAH S. FERGUSON 



would seem to indicate was the case. The whole system may be 

 readily injected from any one of the ^ih-loops with which it is 

 connected. The true direction of flow is therefore from the effer- 

 ent gill-loops through the commissural arteries to the median 

 hypobranchial and from it to the muscular, pericardial, gastric, 

 esophageal, and coronary branches, with only a relatively insig- 

 nificant and inconstant anastomotic supply from the subclavian 

 artery. 



Anastomoses in both the arterial and venous systems, forming 

 "circles" about the body wall and the viscera are of very frequent 

 occurrence in this class of fishes as was pointed out for the venous 

 system by T. J. Parker in 1880 {vide supra). The subclavian 

 artery forms such a circle beneath the coracoid arch and several 

 similar ''circles" are formed by anastomosis between the two sides 

 in the hypobranchial system as well as in other parts of the body 

 with which we are not now specially concerned. The arrangement 

 in the arterial system is therefore very similar to that which Parker 

 found in the venous. 



At the ventral extremity of each efferent gill-loop, at the point 

 where the hypobranchial commissural arteries arise, is a small 

 sinus-like dilatation (figs. 5 and 6, s. a. v.) which obviously serves 

 as a reservoir where the blood coming from the two sides of the 

 loop, which are in adjacent branchial arches, will intermingle, and 

 from this sinus blood is distributed through the commissural 

 arteries (''lateral hypobranchial" of Parker and Davis) anteriorly, 

 posteriorly, or to the median hypobranchial in such proportion 

 as the caliber of the several vessels and the course of the circula- 

 tion dictate. The arterial sinus at the ventral end of the first 

 gill-loop (first ventral sinus) is usually a trifle larger than the 

 others. The thyroid artery arises from the anterior end of this 

 sinus or from the adjacent portion of its anterior limb in the hyoi- 

 dean hemibranch. It arises either as a separate and independent 

 vessel or as a conjoined trunk with the mandibular artery; more 

 frequently, in the specimens I have dissected, it was independent. 

 The artery passes directly forward and inward to the extreme 

 lateral border or angle of the thyroid gland. It continues its 

 path along the surface of the thyroid gland (figs. 3, 4 and 19) near 



