BLOOMER : ON THE BRITISH SPECIES OF THE GENUS SOLEX. 99 



The anterior aorta then turns anteriorly, at which point it gives rise 

 to the pedal artery {P. Ar.) and later to the labial branches, and a 

 branch to each bifurcated anteiior retractor pedis muscle. It then 

 passes underneath the anterior adductor muscle, vascuiarising this and 

 finally dividing in the mantle into two branches. jNIenegaux is of 

 opinion that it continues by the circumpallial, although he has not 

 been able to trace the connection very clearly. 



The pedal artery (P. Ar.) passes to the foot and buries itself in 

 the tissues. It supplies the pedal ganglion, follows the length of the 

 foot dorsal to the anterior pedal sinus, and gives off numerous 

 alternating branches before dividing into two divisions at tlie extremity 

 of the foot. 



Arising from the posterior end of the ventricle is the posterior 

 aorta {P. Ao.), which very shortly after leaving the ventricle forms the 

 dilatation known as the bulbus arteriosus (B. A.). The latter is 

 separated from the ventricle by a small valve, it is of considerable 

 length, and extends to the posterior adductor muscle (P. A.), sur- 

 rounding the rectum like a sheath and attached to it by small muscular 

 columns. 



From the bulbus arteriosus a small artery arises which passes to 

 the dorsal part of the pericardium. 



Near the posterior adductor muscle the posterior aorta divides 

 into the two posterior pallial arteries (P. P. A), one going to the 

 right and the otlier to the left, and both passing underneath the muscle 

 and communicating with the rectal lacunae, these two branches then 

 open into the two pallial sinuses. They further communicate with 

 the tissues surrounding these organs; sinking into the walls, they reach 

 the connected marginal borders of the mantle lobes, passing round 

 these, they enlarge very much and give off on the external surface 

 numerous small branches, not a fused network, and finally return 

 anteriorly to the level of the attachment of the dorsal integument to 

 the shell. Owing to the damage sustained in the removal of the 

 animal from the shell, as mentioned above, it has not yet been 

 possible to trace any connection between the anterior and posterior 

 aortae. 



The branches of the posterior aorta are themselves true arteries, 

 but the existence of an endothelium in them has not yet been demon- 

 strated. In all cases these are walled canals exhibiting, laterally, 

 orifices leading to the pallial lacunae. Everywhere in all the arteries 

 of the mantle Menegaux states that he has found this character to 

 exist. 



In the Pelecypoda generally the arteries open into the lacunae, 

 but in the visceral mass of the foot these are only fine ramifications. 



