220 PROFESSOR FRANK J. COLE 
as shown in the second afferent branchial of fig. 1. Generally, also, they are found on 
the posterior surface of the artery, and are hence directed backwards. ‘Their structure, 
which will be described in detail later, varies from a simple papillee with an unbranched 
cavity to an elaborate digitiform structure with a complex cavity. 
The efferent branchial arteries of Mymine (fig. 1, ef: br.) differ from the afferents 
in so far as there are two of them to each gill. In Bdellostoma dombeyi there is only 
one to each gill pouch, but there are two in B. forsterr. In Myxime each afferent gill 
duct (a. g. d.) has an artery immediately in front of and behind it (ef br.). All the 
efferent arteries open into a commissural vessel known as the common carotid (¢. car.), 
which is attached to the side of the cesophagus (oes.), in front, passing straight forwards 
to the head, whilst behind, it rises to open into the systemic aorta (s. ao.) just posterior 
to the sixth gill. The systemic aorta is prolonged forwards in the median line over 
the gut as the anterior systemic aorta (a. s. ao.). 
The common carotid and anterior systemic aorta are connected up by three anas- 
tomoses, and although I have found this number to be very constant, the same three 
are not always present. For example, in fig. 1 the anastomoses are connected with 
afferent gill ducts three, four, and five, but they may be associated with four, five, and 
six. It seems, on the whole, probable that each anastomosis is formed either by the 
fusion of a pair of efferent arteries, or represents the dorsal extension of one. 
It is hardly likely that the common carotid has any existence per se, but stands for 
merely a series of longitudinal anastomoses. ‘This is borne out by the state of affairs 
both in Myaine and bdellostoma. In the former the common carotid usually narrows 
down behind the fourth afferent gill duct (cp. fig. 1), and between the fifth and sixth 
gills it may become so fine a thread as to be almost imperforate. In such a case the 
last two transverse anastomoses are clearly the direct continuations of efferent branchial 
arteries, and the posterior section of the carotid which rises to fuse with the aorta is 
obviously the continuation of the last efferent branchial. 
There are no vascular papille on any part of the dorsal aorta, either in the branchial 
region or anteriorly to it. Dorsally the papille are confined to the common carotids 
(fig. 1), but are by no means restricted to the branchial region. The common carotid 
between the first gill and the division far forwards into external and internal carotids, 
always bears a number of the papille. They are, however, largely confined to the posterior 
four-fifths of this anterior section of the carotid, as the following count, from behind 
forwards, exemplifies: 8, 11,7, 4,2. The pre-branchial papillee are simpler in structure 
than those occurring in the immediate neighbourhood of the gills, and if they open 
externally at all, it must be very rarely. 
It now becomes necessary to describe the spaces into which blood is discharged 
by the afferent and efferent branchial arteries through the agency of the vascular 
papille. In front of the branchial region, 7.e. in the region of the club muscle, there is — 
a large dorso-ventrally flattened lymph sac between the notochord and the cesophagus, — 
but which extends some distance laterally on each side of the gut. The anterior 
