LAWSON, ON LIMAX MAXIMUS. 21 
great pulmonary vein of either side into the numerous lesser 
ramifications of the lung-membrane, and been in this way 
fully exposed to the atmospheric air, it flows in two principal 
directions, according as it has passed from the upper or lower 
borders of the great lateral veins. That which has been sent 
upwards travels in obedience to the limits of the pulmonary 
sac, first superiorly, then horizontally, and finally inferiorly, 
till it gains the external edge of the pericardial gland; and 
conversely, that which left the under surface of the vein 
courses first inferiorly, then horizontally, and eventually as- 
cends, till it arrives at the same position as the rest. Here, 
then, we find all the blood which has traversed the respiratory 
reticulation at one period or other of its career, and from 
this it passes internally, through the pericardial gland, in a 
perfectly centripetal manner, till it has reached its inner 
border; this latter expands, and constitutes, by a double, 
sector-like fold of membrane,—whose arc is confluent with the 
anterior division of the gland, and the junction of whose sides 
is intimately attached to the heart,—a capacious sinus. Into 
this expansion the blood is next introduced, flowing readily 
into it at its immediate union with the gland, and being con- 
veyed from the posterior ternal border of the latter by a 
canal partly circular, whose concave edge lies against the 
heart, whose convexity is continuous with the gland, and 
whose two orifices open into the lacunal cavity referred to. 
From the sinus the blood is transmitted to the heart by an 
aperture of communication between the former and the base 
of the latter. Finally, by the contractions of the heart it is 
propelled onwards through the aorta and its divisions (regur- 
gitation into the sinus being prevented by a small fold of 
membrane acting as a valve) to the different systems of organs, 
and so on, as before. The heart is a thin muscular bag, of a 
somewhat triangular or pyriform description, and of a faintly 
marked fiesh-like colour; it is placed in the thoracic region, 
being surrounded by the pericardial gland, bounded below 
by the fibrous membrane separating the heart-chamber from 
the visceral sac, and above by the floor-tissue of the shell- 
bag; it lies obliquely, its apex pointing backwards and to the 
right, and its base in the opposite direction. It measures a 
1 inch in length, and + inch or thereabouts in width. It 
is wrong to describe the heart as being composed of an 
auricle and ventricle; it is a simple bag, having but one 
cavity, and not presenting any division, either by constric- 
tion or otherwise. It is almost wholly formed of non- 
striated muscular bands, interlaced in the most complex 
manner, and freely united to each other at their extremities. 
