152 
ANATOMY AND PHYSIOLOGY 
tures, (fig. 2, b.) 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 
©f the lower valve are forced upwards by the in- 
creased 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 dorsal 
vessel, or that -which is divided into separate cham- 
bers furnished with valves, are attached several flat 
triangular muscles, the points of which are fixed to 
the dorsal plate of the abdomen, (Plate III. fig. 1, //.) 
These were called by Lyonnet, rather fancifully, the 
wings of the hearty 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 Bhewn on Plate 
III. fig. 2, a , a, a, interior walls with their circular fibres ; 
6, by the lateral or auric ulo- ventricular apertures ; c, the semi- 
lunar valve ; d, d, interventricular valves. 
