284 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
minute ramifications of this vessel are extended backwards and outwards to the sides 
of the pericardium. In the peritoneum also there is an extensive ramification of cir- 
culatory and tracheal vessels, intermingled with each other in the most complex 
manner. Some of these vessels run parallel with the tracheal vessels, others are 
distributed to the structures covered by the peritoneum, and others pass through the 
peritoneal coverings and are distributed to the organs inclosed by them. 
In the genus Lithobius the number of chambers to the heart, and of leg-bearing 
segments to the body, is reduced to fifteen. The form of the chambers and the 
general distribution of the systemic arteries closely resemble those of Scolopendra, 
but there are some peculiarities that deserve notice. The anterior chamber (fig. 23. 
1 . p) gives off three trunks, as in Scolopendra, but the two lateral ones, instead of 
passing forwards and then arching backwards, as in that genus, pass directly outwards, 
transversely to the chamber, and give off a single large trunk from their sides directly 
into the basilar joint of the great mandibles (c), at the posterior part of the short ba- 
silar segment of the head (b) ; and then unite beneath the oesophagus (r) in the same 
transverse manner, above the great subcesophageal ganglion to form the supra-spinal 
artery ( y ), which commences in this union without receiving a small median trunk 
from the inferior surface of the head, as in the Scolopendra. This artery passes 
backwards, in the middle line above, and between the two separated nervous cords 
( y , y ), and gives off a pair of branches on the ganglions almost precisely the same as 
in that genus. It appears also to form some unions, both anterior and posterior to 
the ganglions, as in the Scorpions, with vessels that exist below the nervous cord, and 
which seem to belong to a portal system. All the blood sent through the aortic 
arches is returned along the under surface of the body in the spinal artery, from 
which it is sent off to the sides of each segment through the lateral trunks, the divi- 
sions of which take the course of the nerves to the muscles, to the legs, and to the 
respiratory organs. Posterior to the fourteenth pair of ganglia in the nervous cords 
the spinal artery (fig. 24.) is divided into two branches (15.) which pass backwards, 
side by side, as far as the anterior margin of the terminal ganglion, at the front 
of which (z) each gives off a branch that passes laterally backwards and outwards, 
and the main trunk then pursues its course over the ganglion on which it gives off a 
second branch (.r) which accompanies the great nerves from this ganglion to the pos- 
terior pair of legs. The remaining portion of each division of the spinal artery then 
divides into several small branches, which accompany the nerves from the caudal 
ganglia (17, 18.) to the external organs of generation and the rectum. The supra- 
spinal vessel in Lithobius is accompanied on each side by ramifications of tracheal 
vessels, distributed along the sides of the cords. From these vessels numerous rami- 
fications are sent to the ganglia, as in insects, and are distributed through their 
structure. When a tracheal vessel is given off behind a ganglion, it sends a branch 
forwards beneath the lateral vessels from the great spinal artery, and it is then divided 
on the upper surface of the ganglion into very minute rainusculi, some of which 
