Spencern—Z%e Blood Vessels of Ceratodus. tl 
D. Vessels arising from the dorsal aorta. 
These vary on the two sides of the body. 
(a) The left side. 
(a) Subelavian (fig. 2). 
This name was originally applied by Dr. Giinther* to the artery in question, and 
it was rightly pointed out by him that the left subclavian was twice as large as the 
right. The vessel arises at the level of the fifth muscle segment behind the scapula. 
Immediately after its origin it divides into two branches :— 
(1) The érachial artery (figs. 2 and 14, 2 ér. art.). This runs outwards, 
downwards, and slightly forwards to the attachment of the pectoral limb. It gives 
off first a branch to the muscles behind the lower part of the coracoid and, as it 
enters the limb, another small branch which runs round to the anterior face of the 
lower part of the coracoid (corac. art. ). 
(2) The anxterzor spermatic (or oviducal) artery (figs. 2 and 14, 2 ant. sperm. art.). 
This is a large branch—larger than the brachial 

which passes backwards almost 
immediately from the point of origin of the subclavian. It runs nearly parallel to 
the vertebral column, crosses the large spermatic vein of the same side, and enters 
dorsally the anterior extremity of the body cavity. Here it passes at once into the 
spermatic band (or the ovary). It gives off branches to this, and at the posterior 
end 7s adtrectly continuous with the posterior spermatic (or oviducal) artery. There is 
no difficulty in tracing this artery along the whole length of the spermatic band, 
though its size is somewhat diminished some distance from the anterior end and 
increases again towards the posterior end. 
(b) Segmental arteries. 
These, as in other forms, are given off in each segment, right and left, from the 
whole length of the dorsal aorta, and supply the dorsal muscles. 
(c) Iliac, renal, posterior spermatic (or oviducal), intestinal, and cloacal 
arteries (figs. 10 and 14). 
From a point somewhat behind the level of the anterior end of the kidneys 
arises a large vessel which divides into the following branches :— 
* Phil. Trans. R.S. London, 1871, p. 511. 
