38 PBOF. HUXLEY ON SOME POINTS IN THE 



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 for- 

 wards 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 com- 

 municate 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 the two divisions of the fifth chamber, the middle, by far 

 the smallest, being alone hitherto known. 



A delicate membranous band passes from the whole length of 

 the middle line of the rectum to the heart and to the ovary. 



The singular " pyriform appendage" of the heart lies in the 

 left process of the ligament, its anterior edge nearly following 

 the arcuated contour of that process. 



The siphuncular process of the mantle was broken in my speci- 



