152 ANATOMY AND PHYSIOLOGY 



tures, (fig. 2, .) and, at the same time, the stream 

 in the centre commences its ascent, as indicated in 

 the drawing by arrows. When the chambers have 

 attained their greatest state of expansion, the sides 

 of the lower valve are forced upwards by the in 

 creftsed flow of the blood from the section below the 

 valve, the lateral openings are closed, and the main 

 current of the blood is projected through the two 

 valves, as shewn in fig. 3, a* 



To each side of the abdominal portion of the dorsa 

 vessel, or that which is divided into separate chain 

 bers furnished with valves, are attached several fla 

 triangular muscles, the points of which are fixed to 

 the dorsal plate of the abdomen, (Plate III. fig. 1, h.) 

 These were called by Lyonnet, rather fancifully, the 

 wings of the heart, and their object is to retain that 

 organ in its place, and probably to aid its contrac- 

 tions and expansions. When of sufficient length, (as 

 in the example figured,) they adhere immediately to 

 the arch of the abdomen, but when short, their attach- 

 ment is by means of a supplementary band of fibres. 



As the part of the dorsal vessel, to which these 

 remarks refer, is regarded as the true heart, so the 

 anterior portion, which is a simple continuous tube, 

 may be considered as representing the aorta. It 

 commences where the valves and lateral muscles 

 terminate, passes through the thorax, and terminates 



* A section of the dorsal vessel is likewise shewn on Plate 

 III. fig. 2, a, a, a, interior walls with their circular fibres; 

 ; A 6, the lateral or auriculo-ventricular apertures ; c, the semi- 

 lunar valve ; d, d, interventricular valves. 



