538 
DR. A. GUNTHER’S DESCRIPTION OF CERATODUS. 
satisfaction of finding my supposition confirmed. In this specimen there are, in the series 
corresponding to the pair of small papillae, four valves (fig. 6, g) corresponding in position 
to, but much smaller than, the permanent large valves which I have described above. 
The conus arteriosus branches off into four arcus aortce (figs. 1 & 5, h, i, 7c, l ) on each 
side, the origins of the two anterior being more on the ventral side, and entirely distinct 
from each other, those of the two posterior being confluent for a very short distance, 
and situated more on the dorsal side. The valves are placed close to, and nearly oppo- 
site, the origins of the arcus aortse, so that one valve corresponds to the common origin 
of the two posterior arches (7c & l), and one to the origin of the first arcus (7i), whilst 
the second arcus (?) has no separate valve opposed to its root. 
These arches diverge, severally entering the ventral end of each of the four gills 
(fig. 8), and, reappearing at the dorsal end (fig. 9), converge again to form the aorta. 
They are united in such a manner that the two anterior are confluent into a common 
stem, and the two posterior into a second. The first arcus, immediately after having 
left the gill, emits a considerable branch as Carotis (n), and a second much smaller re- 
current branch (o), which also enters the brain-capsule on the margin of the basal 
bone (ha). 
The common stem of the aorta is formed opposite the beginning of the narrow pos- 
terior part of the basal bone. Its walls are at its commencement easily compressible, 
and collapse when empty ; however, very soon they are strengthened by firm, tendinous 
bands, which at the origin of the arteria cceliaca are so much developed as to form a 
rigid half-canal covering the ventral side of the aorta. 
The strongest lateral branch of the aorta is the arteria cceliaca (p>), which leaves the 
aorta at a right angle about an inch below its origin : it is present on the right side only ; 
and, as mentioned in the description of the liver, it winds like a collar round the narrow 
neck of that organ, distributing its contents through the intestinal tract. 
At the same place where the arteria cceliaca branches off, aright and left arteria suh- 
clavia (q, q 1 ) take their origin. The right is much narrower than the left, and carries 
blood merely to the fore limb of its side. The left is about twice as strong, sends off a 
small muscular branch, and then divides into two arteries. One of the latter runs 
straight towards the left paddle, emitting two small branches, which enter the foremost 
extremity of the testicle. The second artery forms a very peculiar anastomosis (r) with 
the left vena cava superior (s'). This anastomosis is also indicated on the right side; but 
its arrangement is somewhat different ; namely, the right vena cava superior (s) emits a 
branch (t) inwards, towards the aorta, running parallel with the arteria coeliaca. The 
branch is widely open at its origin, and colouring fluid can easily be injected into its 
cavity from the vena cava ; but the canal is gradually obliterated, and closed entirely 
before it reaches the aorta. Probably there exists an open communication between 
the vein named and the aorta at an earlier period of life. 
The number of intercostal arteries, which are of inconsiderable calibre, has not been 
ascertained. 
