PARKER AND DAVIS : HEART BLOOD VESSELS IN FISHES. 169 
authors are compared it must be admitted that both sets of arteries 
have beeu previously observed. Thus in Raja clavata , Hyrtl (’58, 
p. 16) described and figured the commissural arteries as lying 
between the coracobranchial and coracoliyoid muscles ; hence they 
correspond to what we have called ventral commissurals; and the 
same may be said of the commissural arteries figured in a species of 
skate by Martin (’94, Fig. 7). Dorsal commissurals have been 
figured by Parker (’84, p. 62, Fig. 20) in Iiaja nasuta and by 
Monro (1785, p. 16, Tab. 1, fig. 4) in the species of skate described 
by him. In Iiaja nasuta they are the fifth commissurals and in the 
species figured by Monro they are double and represent commissurals 
of the fourth as well as of the fifth arch. 
The right and left commissural arteries in Raja erinacea converge 
on the root of the ventral aorta, where they may anastomose, as in 
Raja clavata (Hyrtl, ’58, p. 16), or remain unconnected. From 
each commissural artery a coronary artery extends over the bulbus 
to be distributed to the ventricle. The left coronary (PI. 1, fig. 2, 
cor. s.) is larger than the right (cor. dx.) and is distributed in the 
main to the ventral surface of the ventricle; the right extends to the 
dorsal surface of the bulb and ventricle and to the auricle. This 
plan of distribution has already been observed in other Species ( Raja 
clavata , Hyrtl, ’58, p. 16 ; Paja sp.?, Martin, ’94, p. 25 ; Torpedo 
sp.?, Hyrtl, ’58, p. 3). 
From the coracoid arteries in Raja erinacea posterior coronary 
arteries (PI. 1, fig. 2, cor.p.s.) may extend over the ventral face of 
the venous sinus to be distributed to the dorsal face of the ventricle. 
These vessels maybe unilateral (Fig. 2) or paired (PI. 2, fig. 5). 
Similar vessels have been described and figured in Raja clavata 
(Hyrtl, ’58, p. 17) and Raja nasuta (Parker, ’84, p. 61). 
The coracoid arteries in Raja erinacea may give off branches 
which anastomose with what we have supposed may represent the 
sixth commissural arteries (PI. 1, fig. 2, corns, d. vi.) , a condition 
similar to what has already been found in other skates by Monro 
(1785, Tab. 1, fig. 4), Hyrtl (’58, Taf. 2), and Parker (’84, p. 62, 
Fig. 20). 
In Amia calva no trace of lateral hypobrancliials was discover¬ 
able. The arteries which supply blood to the coronaries come from 
the fourth visceral arches, and hence correspond to the fourth com¬ 
missural arteries (PI. 2, fig. 3, corns, iv.). These unite in the 
