122 EDWARD PHELPS ALUS jr., 



to the tendon of the sternohyoideus and then diminishes greatly in 

 size. As it traverses, in this part of its course, a region anterior 

 to the thyroid gland, and as no indication whatever of any branches 

 arising from it could here be found, it seems most improbable that it 

 supplies the thyroid, as Wright says it does, my work thus agreeing 

 with Maurer's work on Teleosts (6, p. 218). Continuing forward, the 

 artery in Amia increases in size, in the sections, and comes to lie 

 between the hypohyal and the branchiomandibularis muscle. Anterior 

 to the hypohyal it turns upward and laterally in the base of the 

 tongue of the fish, and then turns downward, at first mesially and 

 then laterally, and reaches the dorsal surface of the hyohyoideus 

 muscle. There it breaks up into several branches and could not be 

 satisfactorily further followed. A large part of it certainly penetrates, 

 and part of it perforates, the hyohyoideus muscle. 



The afferent artery to the gill cover arises, at this age, with its 

 fellow of the opposite side, as a median vessel, from the ventral sur- 

 face of the truncus arteriosus just as that vessel separates into the 

 afferent arteries for the first pair of branchial arches. Running 

 downward and forward directly through the thyroid it reaches the 

 dorsal surface of the branchiomandibularis muscle, where it separates 

 into two parts, the afferent arteries of either side. Passing downward 

 and forward along the lateral surface of the branchiomandibularis, the 

 artery of each side reaches the level of the ventral surface of that 

 muscle and there turns laterally and forward across the ventral sur- 

 face of the hyohyoideus muscle, near its anterior end. When it 

 reaches the lateral edge of the hyohyoideus it became, on one side 

 of the specimen, so small that it could not be traced, and seemed to 

 entirely disappear. On the other side it there turned backward along 

 the dorsal surface of the hyohyoideus and was traced onward as a 

 relatively important vessel a considerable distance in the gill cover, 

 no attempt being made to trace it to its end. No indication whatever 

 of any branches from it to the thyroid could be found, although it 

 traversed that organ. The thyroid was richly supplied by venous 

 vessels which were in direct connection with what must be the homo- 

 logues of what Field (3) refers to in Axolotl as the jugulares in- 

 feriores, and if the thyroid receives other blood than that transmitted by 

 those veins it seems as if it must be supplied to it by certain small 

 branches that possibly here arise directly from the truncus arteriosus. 

 No such branches could be definitely traced from the truncus, but 



