20 M. E. Claparede on the Circulation of the Blood 



as pneumocardiac vessels conducting the blood from the re- 

 spiratory organs to the pericardium, and consequently indirectly 

 to the lateral orifices of the heart. But this opinion is decidedly 

 false, seeing that these vessels directly reach the heart. Their 

 cardiac origins, which we have described as forming lateral 

 diverticula of the heart, have so little to do with the pericardium 

 that the lateral slits are in part cut in their base. If, therefore, 

 these organs are vessels and not ligaments, they are arteries and 

 not veins, I hesitate the less to pronounce in favour of the old 

 opinion of Treviranus"^, because the existence of lateral arteries 

 of the heart is a desideratum — the quantity of blood issuing 

 through the posterior orifice of the heart being evidently far 

 inferior to that which traverses the anterior regions of that 

 organ. 



The heart and its lateral arteries are the sole arterial vessels 

 of the abdomen. The blood is poured out by them into the 

 interorganal lacunse, and bathes all the organs. The heart 

 itself is bathed by a mass of blood which travels in an opposite 

 direction to that contained in the heart — that is to say, from be- 

 hind forward. This liquid is drawn in through the lateral -ori- 

 fices at each diastole of the heart. I cannot say whether this 

 pericardiac lacuna is the cavity of a pericardium. I have never 

 seen anything that appeared to indicate the presence of such an 

 organ, but I may say that I have rather been led to doubt its 

 existence. The integument of the young Spider presents several 

 tergal arches — vague indications of a dorsal segmentation. Their 

 number appears to be six, or perhaps seven. At each of them 

 is a muscular ligament attached to the heart, no doubt corre- 

 sponding to the muscles called the wings of the heart in Insects. 

 These muscles appear to be attached, on the one hand, to the 

 integuments, and, on the other, to the wall of the heart itself. 

 There is nothing to indicate the existence of a pericardium; 

 moreover it is a question of secondary importance to ascertain 

 whether the blood is here contained in an interorganal lacuna or 

 in a pericardium. The important fact (and this is beyond all 

 dispute) is, that the heart is bathed in all parts by a mass of 

 blood contained in a space which I shall provisionally name the 

 pericardiac lacuna, without, however, attaching any importance 

 to this denomination. A fact which is equally important to 

 note is, that the origins of the lateral arteries to which I have 

 given the name of lateral diverticula of the heart are bathed ex^ 

 ternally by the blood of this lacuna. Now this could not take 



1836, tome vi. p. 355). See also the ^Regne Animal/ editioa illustree : 

 Arachnides, pi. 3. 

 * Ueber den inneren Bau der Arachniden, 1812, p. 28. 



