PARKER AND DAVIS : HEART BLOOD VESSELS IN FISHES. 165 
nal vessel following the course of the ventral aorta. That the lat¬ 
eral and median vessels are not homologous, as is implied in 
Parker’s account, is seen from the fact that in Mustelus, as Parker 
himself (’87, p. 697, PL 34, fig. 1) has shown, both sets of vessels 
may be present. We have, therefore, given them distinguishing 
names: median and lateral hypobrancliials. Moreover, neither of 
these vessels can be properly considered a dependency of the sub¬ 
clavian, for the branch which leaves that artery, and which Parker 
regarded as their root, may be connected with them, as Hyrtl (’58, 
p. 17, Taf. 2) has shown, by only a relatively small vessel. The 
union, then, is not in the nature of a continuous trunk, but an 
anastomosis, and the vessel posterior to this union must be consid¬ 
ered in the light of an independent artery. This we have called 
the coracoid artery. 
In Carcharias littoralis the lateral hypobranchial artery (PI. 1, 
fig. 1 , h’brn. 1.) is a vessel irregular in its course but always con¬ 
nected with the efferent branchials of the second, third, fourth, 
and fifth visceral arches (II-V). 1 It may extend to meet those 
of the sixth arch (VI), but when this occurs, the prolongation is 
usually on one side of the animal only, and the system as a whole 
is unsymmetrical. 
Lateral liypobranchials, essentially similar to those in Carcharias, 
occur in Zygaena malleus and in Mustelus stellatus according to 
the figures given by Hyrtl (’72, Taf. 3, fig. 2, and Taf. 2, fig. 2) 
and in Mustelus antarcticus as figured by Parker (’87, PL 34, fig. 
1). In these three species the vessels are figured as extending 
from the second to the sixth arch. 
Carcharias possesses two or at most three pairs of commissural 
arteries. The most anterior pair lies in the grooves between 
the second and third insertions of the coracobranchial muscles (PL 
1, fig. 1, cc’o brn. 2 and 3) and parallel with the efferent arteries 
going to the fourth visceral arches. We have, therefore, called 
these vessels the commissural arteries of the fourth arch or more 
briefly the fourth commissural arteries (corns, iv). In a corre¬ 
sponding way, fifth commissural arteries (corns, v) can be dis¬ 
tinguished. The fourth and fifth arteries were found in all the 
i In numbering tlie visceral arches we have followed the scheme laid down hy Gegen- 
baur (’98, p. 457), in which the first visceral arch is represented by the upper and lower 
jaws, the second by the hyoid arch, the third by the first branchial arch, the fourth by 
the second branchial arch, etc. 
