280 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
structure, the fibres of which are loosely interwoven with each other. It completely 
incloses the second, or inner tunic, the proper ventricular structure, from which it 
may be separated without difficulty ; and it also forms the external covering of the 
systemic arteries (c) at their origin, and may be traced along them to some distance 
from each chamber. The action of its fibres seems to be chiefly in the longitudinal 
direction, and thus to assist mainly in shortening the vessel. The inner tunic is 
formed of two sets of muscular fibres. The inner one of these, covered by a delicate 
membrane, lining the ventricle, consists of longitudinal fibres, which are most per- 
fectly developed on its upper and under surfaces, and which are extended throughout 
its entire length, from the posterior segment to the head. The other set (e), which 
is external to this, is formed of numerous short, broad, transverse muscular bands, 
very much resembling in appearance the cartilaginous rings of the trachea in verte- 
brated animals. These transverse muscular bands are thicker and stronger than the 
longitudinal fibres, and form the sides of this tunic. They do not completely encircle 
the longitudinal ones, but pass only half-way round, on each side, having a space 
between those of the two sides, both on the upper and under surface. This space 
is occupied by the principal longitudinal fibres, to the sides of which the extremities 
of these transverse bands are approximated. They are not, however, all arranged in 
one parallel longitudinal series, but are placed alternately nearer to, or more distant 
from the median line. This arrangement of the transverse fibres may perhaps be of 
great importance in the action of the vessel, since the inequality and the necessarily 
varied direction of the forces of the successive contractions of these fibres must 
occasion a spiral or peristaltic motion of the whole organ, which may be necessary 
to propel the blood onwards. Physiologically considered, it may be of still more 
importance than is at first apparent, with reference to the structure of arterial vessels 
in the Vertebrata, and their function of conveying the blood ; since not only does this 
arrangement exist in the heart of the Scolopendra, but also in the systemic arteries, 
given off from it in each chamber ; and consequently, by the analogies of comparative 
anatomy, we may reasonably expect to find a similar arrangement, mode of action, 
and function of fibres in the arteries of all animals. The passages into the systemic 
arteries in the Scolopendra are free circular openings ( d ), bounded by these trans- 
verse fibres, the existence of which I have traced in the inner tunic of the arteries to a 
considerable distance from their origin. These openings are in the infero-lateral sur- 
face of the enlarged posterior part of each chamber of the great auriculo-ventricular 
cavity, into which the blood is poured, through the auricular orifices, on the dorsal 
surface. The auricular orifices pass close together through the internal tunic on its 
dorsal surface, a little posterior to the outlets of the systemic arteries on the under 
surface. From their postero-lateral margin a series of oblique fibres passes diagonally 
forwards, in the interior of the chamber, until meeting in the middle line they form a 
double valve, with its apex directed forwards, very similar in appearance to the tri- 
cuspid valve in the heart of Mammalia. This valve is extended forwards from the 
