26o ELEMENTARY BIOLOGY. [CHAP. 



with the instrument as you cut, in order to avoid the 

 possibility of injuring the underlying vessels. Care- 

 fully remove the lateral body wall of the above seg- 

 ments to the level of the middle line, and without 

 dissecting further, note — 



a. The supra-intestinal and supra-neural vessels, to- 

 gether with such of their branches as have been 

 already mentioned. 



Look out for the lateral-neural vessels. 



b. The sub-neural vessel, a delicate median-ventral 

 trunk, seen on raising the nervous axis, to which it 

 is closely applied. 



c. The sub-ifttestinal vessel, a small median longi- 

 tudinal trunk buried up in the ventral wall of the 

 alimentary canal. It may best be seen on gently 

 displacing the gizzard, the walls of which are 

 white. Examine under a lens ; it will be found 

 to be connected with the supra-neural trunk for 

 each segment, by two or three delicate commissures. 



d. The circumcesophageal vessels ; six in number and 

 usually greatly distended. (Cf i a.) They lie in 

 segments 6 to ii, and connect the supra-intestinal 

 and supra-neural trunks. 



e. The lateral-ossophageal vessel, a conspicuous usually 

 highly distended trunk, closely applied to the wall 

 of the oesophagus on either side. Large branches 

 of it are seen on the pharynx and oesophageal 

 glands. It runs beneath the latter, and communi- 

 cates with the supra-intestinal trunk in segment 12. 



d. and e. are the most conspicuous vessels in the 

 whole system, and their general relations can be 

 well seen if dissected from beneath. 



