CRUSTACEA. 335 



venous sinus (a) occupies the cephalic region, and covers the sto- 

 mach ; another cavity (b) lies immediately above the heart ; and a 

 series of smaller chambers (c, c, c, c) are situated above the muscles 

 of the caudal region. These cavities, notwithstanding their appa- 

 rent extent, are very shallow ; so that, upon a transverse section, 

 their dimensions are by no means so great as a superficial view 

 would indicate. The sinus (Z>), or that placed immediately over 

 the heart, communicates with that viscus by short trunks, the termi- 

 nations of which in the heart are guarded by valves (fig. 157, 

 /,/,/) so disposed as to allow the blood to pass from the sinus 

 into the heart, but prevent its return in an opposite direction. 



(371.) Such is the apparatus provided in the lobster for the cir- 

 culation of the blood. Our next inquiry must be concerning the 

 course that it pursues during its circuit through the body. 



Messrs. Audouin and Milne Edwards,* after very minutely 

 examining this subject, came to the conclusion that the heart is 

 purely of a systemic character, being only instrumental in propel- 

 ling the blood through the body, but having nothing to do with 

 the branchial circulation ; they conceived that the circulating fluid, 

 having been collected in the venous sinuses, was brought to the 

 roots of the branchiae, over which it was distributed by venous 

 tubes, and then returned to the heart by vessels which they call 

 branchio-cardiac to recommence the same course. The appended 

 figures, however, which are accurately copied from engravings of 

 the Hunterian drawings in the collection of the Royal College of 

 Surgeons,-)- wou ^ seem to gi ye great reason to doubt the accuracy 

 of the conclusions arrived at by the eminent naturalists referred 

 to ; and to show that the heart, instead of being purely systemic, is 

 partly branchial, and impels the blood, not through the body only, 

 but also to the respiratory organs. This view of the subject, 

 which we are disposed to consider as the most correct, is exhibited 

 in the diagram annexed. Setting out from the heart, we find that 

 the blood goes to all parts of the body through the different 

 arterial trunks, and by the great sternal artery (Jig. 157, k) is con- 

 veyed to the legs, foot-jaws, and false feet. But from this same 

 artery (m), vessels, o, o, o, o, are furnished to the branchiae. The 

 branchial arteries so derived (Jig. 159, g) subdivide into secondary 



* Recherches Anatomiques et Physiologiques sur la Circulation dans les Crustaces. 

 Annales des Sciences Nat. tora.ii. 



t Catalogue of the Physiological Series of Comparative Anatomy contained in the 

 Museum of the Royal College of Surgeons ; vol. ii. 



