470 ALFRED GIBBS BOURNE. 



enteric sinus which is but slightly broken up in the Rhynco- 

 bdellidae. 



As might be expected from the absence of the perinephros- 

 tomial sinuses, the cardio-dorsal branches are absent anteriorly 

 to the first testes. 



TheVesselsofthe Gastro-i leal Intestine, and of the 

 Dorsal Sinus. — The vessels of this portion of the alimentary 

 canal arise exclusively from the five large anastomotic arches 

 which are formed above it by the anterior branches of the 

 latero-dorsal vessels. Each of these furnishes two trunks 

 which descend parallel to one another, the one on the right, the 

 other on the left side of the intestine, and each terminates by 

 forming a nearly rectilinear longitudinal vessel ; these vessels 

 occurring on either side of the intestine give numerous bran- 

 ches to its walls. They may be termed collateral arteries. 

 Their branches penetrate the intestinal wall, ramify in the 

 spiral valve, and give rise to a vessel which runs along the 

 whole length of the free edge of the valve. 



The capillaries of this vessel (marginal vessel of the 

 spiral valve, Gratiolet) open into two median longitudinal 

 sinuses, situated, the one immediately above, the other imme- 

 diately below the intestine. 



The inferior of these communicates with the superior in front 

 of the gastric dilatation by two symmetrical branches, which 

 surround the strangulated portion of the canal which terminates 

 the crop in front of the stomach. 



The superior of these two, opening in front into the dorsal 

 sinus, divides posteriorly into two branches, which, passing 

 down at the sides of the rectum, open into the dilatation of the 

 ventral sinus, which lodges the last ganglion of the nerve 

 cords. 



Thus a direct communication is established between the 

 dorsal and ventral sinuses. 



The Dorsal Sinus (fig. 62, and woodcut, fig. 4, d. s.). — 

 This sinus extends above the alimentary canal, along the entire 

 length of the body. - It has no communication with the ventral 

 sinus by means of the abdomino-dorsal branches of the latter. 



