MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. iSl 



The left posterior columella! artery runs forward and upward to the dorsal edge of the left 

 shell muscle near its attachment. After giving off a branch to the dorsal portion of the body 

 wall it bends downward alone- the inner surface of the shell muscle, giving off numerous branches 

 which enter the muscle. 



The right posterior columellar artery arises from the right sideof the aorta about 5 millime- 

 ters anterior to the origin of the hepatico-columellar artery. Since the posterior portion of the 

 aorta is upon the left side of the body cavity, the right posterior columellar artery is considerably 

 longer than the corresponding left artery. The course of the right posterior columellar artery is 

 the same, only inverted, as that of the left. 



About 20 millimeters anterior to the origin of the last artery the right pallio-nuehal artery 

 arises as a branch of the aorta. The left pallio-nuehal artery arises from the aorta -t or 5 milli- 

 meters anterior to the right pallio-nuehal. These arteries pass upward and outward to the dorsal 

 side of the body, entering the body wall at the base of the mantle fold where the latter crosses 

 the dorsal edges of the shell muscles. Several branches leave the pallio-nuehal arteries at this 

 point. Some of these pass into the dorsal portion of the mantle lying against the involution of 

 the shell. The main portion of each artery is continued in the thin wall of the dorsal nuchal 

 region, supplying especially the crescentic fold upon the posterior face of the hood. As it 

 passes along the edge of the shell muscle it appears to send some small branches into the tissues 

 of the muscle. A considerable branch extends into the crus of the funnel. From the outer side 

 of the pallio-nuehal artery a branch enters the mantle, which becomes continuous with the 

 marginal pallia] branch of the anterior pallial artery. 



Usually no other vessels arise from the aorta until it divides into the innominate arteries. 



The anterior proventricular arteries, supplying blood to rather more than the anterior half 

 of the proventriculus, frequently arise from the junction of the aorta with the innominate 

 arteries. These arteries are. however, extremely variable in their position, a fact to which 

 Willey has called attention. One or both may arise from the innominates, or one may be 

 entirely absent. In Willey's Fig. 23 (1896, 1), the left anterior proventricular artery arises from 

 the aorta a considerable distance below its division into the innominate arteries. Two small 

 arterioles going from the anterior proventricular arteries to the walls of the aorta show also 

 considerable variation in their points of origin. Ordinarily one arises from the base of each 

 proventricular artery. In the case figured by Willey both arterioles arise from the right 

 anterior proventricular artery, the left proventricular artery being absent in this case. 



The buccal artery usually springs from the right innominate close to its separation from the 

 left. It passes forward upon the dorsal side of the buccal mass, presently dividing into three 

 branches. The median branch, the superior mandibular artery, runs straight forward in the 

 median line of the buccal mass, giving off branches to the superior mandibular muscles. The 

 lateral branches first pass outward to the sides of the buccal mass, giving off on the way several 

 small branches posteriorly to the mandibular muscles, then turn forward and pass into the 

 buccal membrane and its papilla?. Of the origin of the buccal artery AYilley' says: "It is a 

 singular fact that the great median buccal artery always springs from the right innominate artery. 

 The constancy of this origin would seem to indicate that it is potentially a paired structure." I 

 have dissected specimens in which the buccal artery sprung from the junction of the innominate 

 arteries; in other words, was median. Either position, lateral or median, may be secondary, 

 resulting from a displacement of the base of the artery during growth, and it is difficult to decide 

 which is primitive without the evidence of embryology. 



Five or six millimeters from their junction a branch arises from the anterior side of each 

 innominate (the inferior mandibular artery), which runs forward on the under side of the buccal 

 mass to the muscles and organs of the floor of the pharynx. These arteries are closely bound 

 to the buccal nervous system, careful dissection being required to separate the nervous from the 

 arterial elements. The inferior mandibular arteries supply not only the lower parts of the 

 mandibular muscles but also the tongue and the radular sac, the processes anterior to the tongue, 

 and the salivary processes. 



