246 THE VITAL FUNCTIONS. 



growth, has elucidated many obscure points in 

 the physiology of this important class. It ex- 



and upwards of the inner coat, or coats of the artery," (by which 

 he means the dorsal vessel) " and the under one by a contraction 

 or projection of the like parts of a portion of the artery beneath, 

 so as to come within the grasp of the lower part of the valve 

 above it." The whole vessel is made up of three coats, the two 

 innermost of which, the lining, or serous, and the muscular, or 

 principal portion of the vessel, constitute the reflected portions, or 

 valves ; while the third, or outermost coat, which is exceedingly 

 thin and delicate, is continued over the vessel nearly in a straight 

 line, and does not appear at all to follow the reflexions of 

 the other two. In the caterpillar, this portion of the vessel has 

 eight pairs of small suspensory muscles, seen along the upper side 

 of Fig, 339, which arise from the middle of the upper surface of 

 each valve, and are continued back to be attached over the middle 

 of the next valve : they seem to have considerable influence over 

 the contractions of the valves. The Aortal, or anterior portion 

 of the vessel, extends from the hinder part of the fourth segment 

 to its termination and division into vessels, to be distributed to the 

 head, which division takes place after it has passed the oesopha- 

 gus, and at a point immediately beneath the supra-oesophageal 

 ganglion, or brain of the insect. This portion of the vessel is 

 much narrower than the dorsal, has no distinct valves, or muscles ; 

 nor do any vessels enter it laterally ; but it is very delicate and 

 transparent, and gradually diminishes in size from its commence- 

 ment to its anterior termination. Its course, in the caterpillar, 

 is immediately beneath the integument, along the fourth and 

 third segments, till it arrives at the hinder parts of the second 

 segment ; when it gradually descends upon the oesophagus, and, 

 immediately behind the cerebral ganglion, gives ofl?" a pair of ex- 

 ceedingly minute vessels. It then passes beneath the ganglion, 

 and, in the front part of the head, is divided into several branches, 

 as noticed by Mr, Newport in the anatomical description he has 

 given of the nerves of this species of Sphinx : (Phil. Trans. 183'2, 

 p. 385.) These branches are best observed in the chrysalis (Fig. 



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