BLOOD SYSTEM 455 



thus joins a ring vessel and, since this lies immediately above the nerve ring, I have 

 called it the supraneural ring or artery. 



The anterior part of the supraneural artery is provided with a complex of muscles 

 (Figs. 4 A, 5) attached partly to the endosternite and partly to the ectoderm of the 

 oesophagus. One of these consists of a thin sheet of myofibrils developed in its roof 

 running from the prong of the endosternite to the aortic tendon. I have called it the 

 aortic-endosternite muscle. The endosternite prongs turn outwards at an angle about 

 the middle of their length and, along the inner edges of the distal halves, are attached 

 the aortic-endosternite muscles. 



A narrow strip along the inner edges of these muscles appears to contain myofibrils 

 which differ from the remainder of the muscle. The latter are striated, but the former 

 are homogeneous and stain a very bright red, which contrasts clearly with the purplish 

 red of the rest of the muscle. They appear to be of the same type as the musculature 

 I shall describe (p. 463) for the gut. These narrow strips converge on the middle point 

 of the aortic tendon and join the aortic muscles. 



At a region just behind and slightly lateral to the attachment of the aortic muscles, 

 two muscles originate which pass backwards dorsal to the aortic-endosternite muscles 

 and then extend down the oesophagus to end against its cuticular lining. These 

 I have called the anterior aortic-oesophageal muscles. Each splits into two portions, 

 one of which extends round the sides of the oesophagus and passes down its posterior 

 side. The second extends straight down the front of the oesophagus and crosses from 

 one side of the body to the other. 



From the hinder margin of the aortic tendon, on either side of the frontal apodeme, 

 a pair of muscles, the posterior aortic-oesophageal muscles, run directly down the front 

 of the oesophagus. 



All the aortic-oesophageal muscles insert themselves between the circular muscles, 

 pass through the longitudinal muscles, and attach to the cuticular lining of the oeso- 

 phagus. 



A pair of valves occur in the supraneural ring (Figs. 4 A, 5, and Plate VII, fig. i , c) on 

 either side at the level of the hinder face of the oesophagus. Each consists of a muscular 

 curtain hanging down from the roof of the artery. The muscle is attached anteriorly to 

 the wall of the mandibular artery and, in curving upwards over the supraneural vessel, 

 it passes obliquely backwards and inwards. It narrows down and curves ventrally to 

 attach to the hinder of the muscles which pass through the nervous mass behind the 

 tritocerebral commissure. Contraction of this muscle must pull down the muscle cur- 

 tain so that it presses against the floor of the artery and blocks the passage. This can 

 be seen in Plate VII, fig. i, in which that part of the supraneural artery proximal to 

 the heart is empty, but on the distal side of the valve there is a mass of coagulated 

 blood. 



The antennal arteries extend laterally and then forwards into the base of the limbs 

 (Fig. 11). On entering they apparently divide into two. The outer, smaller branch, 

 appears to open into the cavity of the limb, but the inner can be followed into the cyto- 



