14 
with the hypobranchial of the opposite side; this latter hypobranchial 
having its origin from the subelavian artery of its side but having no 
connection either with the efferent arteries of that side or with ven- 
tral prolongations of those arteries. From the continuous vessel 
formed by this anastomosis, as it passes ventral to the truncus arteriosus, 
either a single median coronary artery has its origin, or two coronary 
arteries, one on either side. 
In Arrzen’s figure, the external lateral hypobranchial above 
described has its origin from a ventral prolongation of the anterior 
efferent artery of the third branchial arch on the left instead of the 
right hand side of the body, and it is shown having a similar origin 
in his drawings also. In these drawings the artery is shown crossing 
ventral to the truncus arteriosus, there giving off three coronary 
arteries and then becoming the hypobranchial of the opposite, or 
right hand side, no hypobranchial being shown on the left hand side. 
On the right hand side there is a ventral prolongation of the efferent 
artery of the third branchial arch, similar to the prolongation on the 
left hand side, but on this right hand side the artery simply supplies 
the coraco-branchialis muscle of its own side and is not prolonged 
into an external lateral hypobranchial. 
In each of the four branchial arches, the epibranchial artery 
appears as the direct prolongation of the related anterior efferent 
artery, and these epibranchial arteries fall into the aorta as shown in 
Atten’s figure, the third and fourth arteries uniting to form a 
common trunk which falls into the median dorsal aorta, while the 
first and second arteries fall independently into the lateral dorsal 
aorta. Slightly posterior to the common trunk of the third and fourth 
epibranchials, the dorsal aorta gives off a median caeliaco-mesenteric 
artery, and, on either side, a subclavian artery. On each subclavian 
artery, near its base, in each of the three specimens examined, there 
is a swelling, apparently formed by a simple thickening of the arterial 
wall; but what the cause of this thickening can be, or what its 
significance, could not be determined. Immediately posterior to the 
subclavian artery, and also immediately posterior to the common trunk 
of the third and fourth epibranchials, a vertebral artery has its origin, 
on either side, and, entering the spinal canal, falls into the median 
myelonal artery. From the fourth epibranchial a small dorsal bran- 
chial muscle has its origin, and from the second epibranchial three 
such arteries arise, one of them being a large and important vessel, 
