17b PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
of being homologous, and since the arteries constitute an integral 
part of this system, it seems improbable that they alone should 
have undergone such fundamental replacements as is implied by 
Martin’s observations on the frog. Possibly the condition in the 
Amphibia is to be explained on the basis of coenogenetic changes. 
However this may be, the whole question of the homology of 
the coronary arteries in higher and lower vertebrates seems to us 
to demand much more extensive comparative study, both anatom¬ 
ical and embryological, than has thus far been accorded to it, before 
a final answer can be reached. 
Summary. 
1. Vessels of Thebesius have been found to open into the auri¬ 
cle of Carcharias, and of Raja and into the auricles and ventricles 
of Amia. These vessels communicate more freely with the coro¬ 
nary veins than with the coronary arteries. They are homologous 
with the similarly named vessels in mammals. 
2. The superficial veins of the heart in Amia, and particularly in 
Raja and in Carcharias, are arranged in three groups corresponding 
to the right coronary vein, the left coronary vein, and the middle 
cardiac vein of mammals. These three groups of veins in fishes 
open into the venous sinus and thus agree in this respect with the 
similarly named mammalian veins which open into the right auri¬ 
cle into which the venous sinus has been incorporated. The 
above mentioned superficial veins of the fish’s heart are homologous 
with those in the mammal’s heart. 
3. The ventral ends of the efferent branchial arteries in fishes 
may be connected by a lateral liypobranchial artery. From this, 
commissural arteries may pass towards the median plane; these 
may be either dorsal or ventral as in Raja, and the dorsal ones 
may be serially arranged corresponding to the fourth, the fifth, and 
possibly the sixth visceral arches, as in Carcharias and Raja. 
The union of the right and left commissurals gives rise to a median 
liypobranchial from which coronary arteries (anterior) are given 
off. These coronary arteries differ from those in mammals chiefly 
in the remoteness of their point of origin. This, however, does 
not necessarily preclude homologizing them with the coronary arte¬ 
ries in mammals. 
Posterior coronary arteries were found only in Raja and have no 
homologues in mammals. 
