166 ALEXANDER PETRUNKEVITCH 



often called alary muscles, are the alary ligaments. Their liga- 

 mentary nature has been elucidated by Causard. They are 

 directed at almost right angles to the longitudinal axis of the 

 heart. Distally they are not attached to the body wall, as 

 usually stated, but merge with a layer of connective tissue, evi- 

 dently representing the splanchnic coelom covering and separat- 

 ing the diverticula of the midgut from other organs situated above 

 the latter. The fourth pair are the hypocardiac ligaments. 

 They are by far the strongest and longest, and are easily mis- 

 taken for muscles, especially where they intercross with the dorso- 

 ventral muscles. From here on they continue diverging and 

 unmistakably and finally merge with the splanchnic layer of 

 connective tissue which covers the diverticula of the midgut 

 from below. The first group of ligaments consists of two pairs 

 only. The epicardiac ligaments are attached to the anterior 

 edge of the first tergite. The hj^Docardiac ligaments are more or 

 less normally developed, but the pteripyles and alary hgaments 

 are wanting. 



Since there are no muscles for the dilatation of the heart, diastole 

 is accomphshed through the elasticity of the heart ligaments. 

 This explains why the muscularis of the heart is so powerfully 

 developed. During systole the heart has to overcome the re- 

 sistance of the ligaments, while the contraction of the latter dur- 

 ing diastole is not impeded by the relaxed muscles. There is 

 nothing unusual in such arrangement, as a similar condition exists 

 in almost all joints of the appendages in Arachnida, where flexing 

 is accomphshed by muscular contraction and extension by the 

 elasticity of the interarticular chitinous membrane. I have 

 counted 120 pulsations of the heart in one minute. 



The pericardium appears as a thin membrane, and the space 

 between it and the heart is, in sections, invariably filled with 

 coagulated blood plasm, and consequently is clearly discernible. 

 Owing to the presence of epicardial and hypocardial hgaments, 

 this space is subdivided into four regions which may be termed 

 sinuses, though they coraanunicate with each other in those re- 

 gions of the heart where there are no ligaments. The lateral 

 sinuses are the largest, next in size is the ventral sinus, while the 

 dorsal sinus, almost round in shape, is the smallest of the four. 



