28 G 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
union of the chambers has actually commenced, it is yet very imperfect, and the 
original divisions between them are still evident, and the systemic arteries pass off 
from their sides as in their imperfect state of development. But very little blood 
enters at the auricular orifices, which still exist in these unions. The chief part now 
enters through the large auricular orifices of the chambers in the middle of each 
dorsal plate. These are very distinct, but are placed more transversely to the heart 
than in Scolopendra, corresponding to the more obtuse form of each chamber, and 
the more compact general form of the whole heart. Here then in the gradual reduc- 
tion of the number of the chambers, their compact form, and the shortening of the 
organ, we trace the stages of the formation of the heart in insects, in which there are 
seldom more than eight chambers. 
The minute anatomy of the heart exhibits also a more perfect state of develop- 
ment than in any of the other Myriapoda. The two tunics of which it is composed 
are united more firmly together, the longitudinal fibres are less distinct than the 
transverse, which are very strong and powerful, and distinctly marked in the ex- 
ternal tunic. The great contractile power of the heart seems to exist chiefly in the 
transverse fibres, the longitudinal contractions being greatly influenced by the sus- 
pensory muscles and the alee cordis. 
The distribution of the vessels in Scutigera closely resembles that of Lithobius ; 
three principal trunks being given off from the anterior chamber of the heart, imme- 
diately behind the head, which has assumed in this family the compact form of true 
insects, the great basilar segment, to which the mandibles or foot-jaws are attached in 
Scolopendra, and the other genera, reduced to a very narrow short segment in Litho- 
bius, being now united to the chief portion of the head in this genus. The aortal 
arches, in consequence of the union of these segments, pass around the oesophagus to 
unite beneath it, immediately behind the occipital portion of the head, while the small 
median trunk is situated entirely within this region of the body, thus affording further 
proof of a higher grade of development than that which we have already seen in the 
Chilognatha. 
The circulatory system in Arachmda has already engaged the attention of several 
anatomists, but hitherto has been only very imperfectly understood. Treviranus 
in 1812 described it vaguely, and first noticed the structure, now described as the 
supra-spinal artery, as part of the nervous system, and considered it a peculiarity 
of the nervous system of the Scorpion. Muller, as before stated, noticed the same 
structure in 1828, but regarded it as a ligament. Both these anatomists entirely over- 
looked the extensive distribution of vessels from the anterior extremity of the heart 
in the cephalothorax. 
The Heart . — The heart (PI. XIV. and XV. figs. 27 and 33. K) of the Scorpion is a 
strong muscular organ, extended along the middle of the back, from its continuation 
with the great caudal artery (q), in the last segment of the abdomen, to the com- 
mencement of the aorta (a) at the diaphragm (j?), that divides the abdomen from the 
