57 



closes the great loi-anieii , and iiuuiediately gives (jff two branches: one, the 

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

 and tnrnis ;in arterial ring around the pupil undei- the iris supiilying the eye 

 and the white-bodies: the second, the pharyngeal (11'). occupies the venous 

 canal \vith the oesophagus and salivary duct and supplies the pharynx. After 

 the artery nf the ring has given off' those branches it passes downward between 

 the pleural and visceral ganglia and enters the fascia between the pedal and 

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

 the sii)honal nerves to the muscles and glands of the humel . it turns forward 

 beneath the pedal ganglion to meet its mate and form the pedal artery. This 

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

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

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

 muscles of the i)harynx . 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 

 lirst arms. The small arteries (jf the arms I'adiate from the brachial artery 

 which lies in the central canal with, and on the i_)uter side of the brachial 

 nerve. The distribution of the branches of the pedal 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 Gknital 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 backward between the adherent walls of the 

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

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

 passes backward along the ujjpei- suiface of the testis or (_)var>- to which it gives 

 off pinnately arranged branches. 



The Posterior A(jrta. 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. 

 Foui- oi- five small vessels arise bom the aorta. Two branches arise together 

 near its origin: (jne (1-| passes thru the nephi-idio-coelomic wall to the ink-sac 

 and to the nephridia, being detlected to the left to pass the inte.stine : the 

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



