36 



that appears to be exclusively distributed to the mucous organ of the oviduct, 

 which is attached to the inside of the mantle just above the pericardium. The 

 artery then sends off a small branch (14. pi. 5. & 6.), wliich winding round to 

 the ventral aspect of the A^entricle (to which it is connected by a process of 

 membrane) passes through a foramen in the septum which divides the pericar- 

 dium from the ca\dty at the bottom of the paUial sac, is then continued through 

 that caiaty, passing between the ovary and gizzard, and lastly enters, without 

 diminution of size, the membranous tube that traverses the partitions of the 

 shell. The tliird and last branch of the lesser aorta runs in the membrane or 

 mesenteiy, between the last loop of the intestine (15. pi. 4. 5. & 6.). 



The larger aorta passes downwards between the gizzard and ovary, and ren- 

 ders to both these viscera. It then winds round along the bottom of the sac, 

 sends off large branches to the liver, and gains the dorsal aspect of the crop, 

 along which it passes (19. pi. 4.) to the oesophagus, distributing branches on 

 either side to the great sheU-muscles. Ha\-ing reached the cerebral chord, it 

 divides into two equal branches (20. pi. 4.), w^hich pass by the sides of the 

 oesophagus through the nervous collar, and terminate by furnishing branches to 

 the mouth, the surrounding parts of the head, and the funnel. 



In order to facihtate the tracing of the arterial system, both vessels arising 

 from the heart w^ere injected with mercury, by which means the small siphun- 

 cular artery was discovered, which otherwise might have remained undetected, 

 or at least of doubtful existence. The coats of the vessels were strong enough 

 to bear a pressure of five inches of mercury without rupture ; and more force 

 was not employed, as this was found sufficient for aU the purposes of the exa- 

 mination. 



§ 5. Of the Nervous System, and Organs of Sense. 



The nervous system of the Pearly Nautilus, though analogous, is in many respects 

 inferior to that of the Dibranchiate Cephalopods. The part which corresponds 

 to the brain of the Cuttle-fish is neither enlarged, nor lobulated, nor contained in 

 a cartilaginous receptacle ; but is a simple rounded chord or commissure ( 1 . fig. 1 . 

 pi. 7.), placed transversely above the oesophagus, and connected at its extremities 

 to the great ganglions. These are six in number ; are disposed symmetrically 

 about the oesophagus, and, together with the central commissure, are loosely 



