57 



closes the great tdiamen, and iinmediatelj^ gives off two branches: one, the 

 optic (9^) , passes with the optic tract through the lateral foramen of the skull 

 and forms an arterial ring around the pupil under the iris supplying the eye 

 and the white-bodies: the second, the pharyngeal (IP), occupies the venous 

 canal with the oesophagus and salivary duct and supplies the pharynx. After 

 the artei'v of the ring lias given oft tliese branches it imsses downward between 

 the pleiu'al and visceral ganglia and enters the fascia between the pedal and 

 visceral ganglia and having given off the siphonal artery (10^) which passes with 

 the siphonal nerves to the muscles and glands of the funnel , it turns forward 

 beneath the pedal ganglion t(.) meet its mate and form the pedal artery. This 

 artery (12') lies upon the upper surface of the jiosterior process of the skull 

 beneath the pedal and pro i)edal ganglia. Near the latter, the following branches 

 are distributed : an artery to the propedal ganglia : a pair of arteries to the 

 muscles of the pharynx , and a median vessel to the tentacular sac. At the 

 ventral end of the propedal ganglion the pedal artery forks and the branches 

 pass forward as far as the middle of the pharynx and then each terminates in 

 three branches : one enters the fifth arm : another enters the fourth arm : and 

 the last passes upward around the pharynx to supply the third . second . and 

 first arms. The small arteries of the arms radiate from the brachial artery 

 which lies in the central canal with, and on the outer side of the brachial 

 nerve. The distribution of the branches of the ]3edal artery is parallel to the 

 distribution of the nerves from the pedal ganglion and so adds evidence that 

 the arms are a part of the foot. 



The Genital Aorta. The genital aoita arises from the middle of the ventral 

 surface of the heart and , having given small branches to the pancreas and 

 peritoneum . it runs downward and backw^ard between the adherent walls of the 

 stomach and caecum. The position of this vessel is constant in the Oigopsida 

 and Myopsida but in the former it arises from the posterior aorta. The aorta 

 passes backward along the upper surface of the testis or ovar>' to which it gives 

 off' pinnately arranged branches. 



The Posterior Aohta. The posterior aorta is about as long as the heart 

 and lies in the partition between the dorsal lobes of the nephridial sac. In the 

 male it is separated from the pallial chamber by the body wall alone but in the 

 female the large nidamental glands also lie between it and the pallial chamber. 

 Four or five small vessels arise from the aorta. Two branches arise together 

 near its origin: one (1-) passes thru the nephridio-coelomic wall to the ink-sac 

 and to the nephridia , being deflected to the left to pass the intestine : the 

 other 1 2^) takes a parallel course in the lower nephridial wall and supplies the 



