294 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
a multitude of anastomosing - vessels before they are distributed on the branchiae. 
These branchiae also receive the second pair of efferent vessels (e), which, like the first, 
pass diagonally backwards from the fibrous structure to the inner side of the branchiae, 
on approaching’ which they are divided, like the other pair, into two branches (m), 
which are subdivided and anastomose with the divisions of the first pair. The 
whole form a most intricate web of anastomosing pulmonic capillary vessels before 
they are distributed on the anterior part of the branchiae. We have thus a complete 
distribution of the blood to the pulmono-branchise in the anterior part of the abdo- 
men. There is a similar but less perfect distribution in the posterior. Besides the 
vessels from the sides of this fibrous structure, which in reality may be regarded as 
a great vena cava, there is also the single vessel extended backwards ( g ) from its pos- 
terior extremity in the median line beneath the nervous cords ( f ) into the abdomen. 
This vessel was formerly described by me*, before I had traced its origin, as the sub- 
spinal vessel. It is extended backwards beneath the nervous cord and receives a small 
vessel from the supra-spinal artery above it, both anterior and posterior to each 
ganglion. Immediately after it has entered the abdomen it gives off a single trunk 
(o), which, joined by a minute vessel from the supra-spinal artery (fig. 29. s), passes 
outwards and downwards on the right side of the cord and a little backwards, lying 
loosely in the under surface of the segment, and at length becomes slightly enlarged 
(o) and is divided into two branches, which also are enlarged at their origin ; and 
the whole form between them in the middle line a triangular dilatation or small vena 
cava ( w ), in which the blood may be accumulated. These branches then pass diago- 
nally outwards and are given one on each side to the anterior part of the second pair 
of branchiae, each being first divided into numerous anastomosing capillary vessels, as 
in those already described. But before this division takes place each branch receives 
the double trunk of two other venous branches (r, s) that convey the blood backwards 
and outwards from the middle inferior surface of the abdomen. These unite with 
the first branch on the inner side of the great vertical muscles (v) that mainly assist 
in the respiratory action of each segment; after which the branch passes backwards 
to its distribution, accompanying the great nerve of the segment (p). When the sub- 
spinal vessel has given off this first pulmonic trunk it passes onward, and opposite the 
middle of the first pair of branchiae gives off a second, which, like the first, is extended 
backwards for a short distance, lying loosely in the segment. This second trunk is 
then dilated and divided into two lateral branches like the first, and these, after re- 
ceiving other vessels from the inferior surface of the segments, are given to the second 
pair of abdominal branchiae. At a little distance further on, when it has arrived at 
the second ganglion of the abdominal cord, the subspinal vessel is itself a little dilated, 
and is divided into two lateral branches which pass outwards in close approximation 
with the nerves from the ganglion ; and having received an accession of venous trunks 
as before, these branches are given to the third pair of branchiae. After this the sub- 
* Medical Gazette, March 10, 1838, p. 971. 
