180 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



which is ovidently pulsatile, but it should not be used in the same morphological sense as in 

 other groups. 



Five vessels arise from the dorsal side of the heart, the courses of which will he described 



presently. 



The heart has thick muscular walls, and in the contracted state consequent upon death a 

 very small tissure-like cavity. The inner surface of the heart is pitted, and by its appearance 

 reminds one strongly of the inner surface of a mammalian heart, though by no means distinctly 

 trabeculated. I have not been able to find anj^ valves at the openings of the vessels leading into 

 or from the heart, except possibly the dorsal aorta. The openings are, however, tightl}' closed, 

 and it is possible that at the commencement of systole the walls of the heart contract first around 

 the openings of the branchial veins, and thus the regurgitation of ])lood is prevented. 



I'^ntil otherwise indicated all references will be to text-lig. 10. 



The largest vessel proceeding from the heart is the dorsal aoi-ta. This arises from the 

 dorsal surface of the heart, on the left side and near the posterior edge. The base of the aorta is 

 conical and possesses thick muscular walls, and could probably be properly spoken of as a conus 

 arteriosus. At the end of the nuiscular portion of the base of the aorta is an elevation of the 

 inner wall, which may be a valve. In some specimens this is (juite distinct and much like a semi- 

 lunar valve; in others it is barely noticeable. Possibly the conical l)ase of the aorta should be 

 considered morphologically as a portion of the heart itself. 



Along the median part of the posterior edge of the heart, dorsally also, arise three small 

 arteries. They lie in the portion of the pallio-visceral ligament attached to the posterior side of 

 the heart. The artery at the left is the artery of the pyriform sac; the middle one is the genital 

 artery, while the one on the right is the gonaducal artery. 



Also from the dorsal side of the heai't. but near the anterior edge, arises the fifth artery, the 

 lesser aoi'ta. 



Let us now follow th(> course of the dorsal aorta and its branches. From its origin on 

 the dorsal side of the heart the aorta extends upward and backward and to the left along the 

 posterior side of the ha^moctelic mem))rane. Turning forward it penetrates the membrane and 

 enters the hajmociel, in which it lies free, running forward over the liver and the oesophagus. 

 In the posterior portion of the ha^moc(el the aorta lies well to the left of the cavity, but as it 

 extends forward it approaches the median line until, near the oesophageal nerve ring, it lies in 

 the median line. Immediatelv liack of the nerve ring the aorta divides into a left and a right 

 branch, the innominate arteries, from which lesser branches are given oft' to the cephalic region 

 and the funnel. 



Conunencing froiu the posterior end of the aorta, the tirst branch leaves it just after the 

 aorta enters the hremocoel. Coming oft' from the right side of the aorta, it runs directly toward 

 the right side of the body, giving oft' tirst a branch anteriorly which passes to the posterior 

 portion of the proventriculus, the posterior proventricular artery; next, a branch posteriorly 

 which iuunediately bends forward and passes around the anterior side of the stomach to the 

 coecum, the cujcal artery; tinally, the end of the artery passes to the stomach, forming the gastric 

 artery, which breaks up into luuuei-ous tine vessels in the walls of the stomach. 



Fi\'i^ or (! millimeters antei'ior to the origin of this arti^ry a much larger artery leaves the 

 left side of the aorta. After a course of about 5 millimeters this artery divides into two branches, 

 the anterior of which goes to the left shell muscle (the left posterior columellar artery), while the 

 posterior branch proceeds to the liver (hepatic artery). I have called the branch of the aorta 

 from which both these arteries arise the hepatico-columellar artery. 



The hepatic artery goes to the junction of the two left lobes of the liver. It divides here 

 into three branches. The left and middles branches enter the left lobes of the liver in which 

 they break up into the tine lobular branches. The right-hand branch of the hepatic artery follows 

 the median coiuiecting portion of the liver to the junction of the two right lobes of the liver. 

 Here it divides into a branch for each lobe. In its course it gives oft' a considerable branch to 

 the median portion of the liver. 



