Muscles of the Heart 73 



The aorta ends in the head by a trumpet-shaped orifice, 

 and here the blood escapes into the body-cavity. 



In the living larva the energetic contractions of the 

 heart are seen to drive the blood along the aorta, and the 

 pulse can be followed by the eye as far as to the fore end 

 of the stomach. The blood with its corpuscles can be 

 seen to stream into the ostia during the dilatation of the 

 heart. 



The muscles of the heaif, when seen from above, are Muscles 



-.- . . , - of heart. 



transverse, except behind the posterior ostia, where they 

 radiate, and become nearly longitudinal (fig. 54). They 

 do not extend completely across the heart, but thin away 

 toAvards the middle line. On the ventral side the muscles 

 have a radiate disposition ; many of them converge 

 towards a median space just in front of the posterior 

 ostia ; none extend completely across. A high power 

 shows that all the muscles of the heart are striated. 



The valves at the beginning of the aorta resemble Aorti.- 



111-1 valves. 



triangular pockets, and when seen irom the dorsal side 

 their pointed tips seem to meet in a point ; a side view 

 shows that this is not really the case ; the tips are 

 separate, and attached to the wall of the aorta by bundles 

 of fibres, rather like the tendinous cords of the mam- 

 malian auriculo- ventricular valves \ 



Six pairs of segmentally arranged alary muscles (so Alary 

 called because they form, as it were, the wings of the 

 heart) are found in the abdomen (fig. 55). As a rule, they 

 spring from the junctions of the segments on the sides of 

 the abdomen : from each junction a muscle passes forAvards 

 and another backwards -. Each muscle expands at its 

 insertion into a triangular fibrous sheet, with numerous 



' Jiiworowski, 1879. 



^ Tho muscle in front of a junction and that behind would together 

 correspond with one alary muscle of a more primitive insect. i^Cf. Miall 

 and Denny, 1866, p. 135, fig. 75.) 



