THE ANATOMY OF THE NAUTILUS POMPILIUS 83 
In fact this cavity may be said to be co-extensive with the 
attached part of the mantle,—the viscera, enclosed within their deli- 
cate “ peritoneal” membranous coat, projecting into and nearly filling 
it, but nevertheless leaving a clear space between themselves and the 
delicate posterior wall of the mantle. 
A layer of the “peritoneal” membrane extends from the posterior 
edge of the muscular expansion which lies between the shell-muscles 
and from the upper wall of the dilatation of the vena cava, and passes 
upwards and backwards like a diaphragm to the under surfaces of the 
gizzard and liver. It is traversed by the aorta, to whose coats it 
closely adheres. 
Along a line nearly corresponding with the horny band which 
proceeds from the insertions of the shell-muscles and encircles the 
mantle below, the pallial wall is produced inwards and forwards into 
a membranous fold or ligament, which I will call the pallio-visceral 
ligament; and this pallio-visceral ligament becoming attached to 
various viscera, divides the great fifth chamber into an anterior 
inferior, and a posterior superior portion, which communicate freely 
with one another. 
Commencing with its extreme right-hand end, the ligament is 
inserted into the line of reflection of the mantle, and then into the 
wall of the oviduct, which becomes enclosed as it were within the 
ligament. The latter then ends in a free edge on the inner side of 
the oviduct, and is continued along it until it reaches the inferior 
surface of the apex of the ovary, into which it is inserted. 
The free edge is arcuated ; and the rectum passes over it, but is in 
no way connected with it. 
Here, therefore, is one great passage of communication -between 
the anterior and posterior divisions of the fifth chamber. 
On the left side this aperture is limited by the heart, whose 
posterior edge is, on the left side, connected by means of a liga- 
mentous band with the surface of the apex of the ovary; but on 
the right, for the greater part of its extent, receives a process of the 
pallio-visceral ligament. Between the ovario-cardiac ligament and 
this process lies the small oval aperture already described by Professor 
Owen, which gives passage to the siphonal artery. It constitutes the 
middle aperture of communication between the two divisions of the 
fifth chamber. 
The left-hand end of the ligament is inserted into the upper wall 
of the dilated end of the vena cava; but between this point and the 
heart it has a free arcuated edge, as on the right side. 
Thus there are in reality three apertures of communication between 
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