VOL. XXVII.] I'HILOSOPHICAL TRANSACTIONS. SQp 



way they push the blood into the heart. The figure of the heart of this ani- 

 mal is almost lenticular; making however three obtuse angles, two on the basis, 

 one to the right, and the other to the left; the third is at the inferior part, 

 where the sinall tendon, which suspends the heart on the level of its basis, is 

 inserted. If this animal be opened alive, we have the satisfaction to see the 

 circulation of the blood, by reason of the transparency of the membranes of 

 the veins, and the alternate motions, or dilatations of the heart and auricles, 

 and the arteries and veins, which are very slow in this animal. 



From the basis of the heart pass out four great arteries, that appear distinctly 

 separated one from the other; whereas in that of the sea tortoise, these arteries 

 are involved, for the length of an inch, in a capsula common to them all, which 

 makes them appear as if they were but one trunk. If these four arteries be 

 entirely cut, the heart is no more suspended, but by the conjunction of the two 

 musculous conduits of the auricles, which pierce the heart in its posterior part, 

 towards the middle of the heart, on the left side; by which the blood runs 

 from the auricles into the ventricle of the heart. These arteries being thus 

 divided, and the heart turned over, the auricles appear lying transversely against 

 the back, in the capacity of the pericardium : they make but one continued 

 fleshy body, a little extended, about two thirds inclining to the left side. It is 

 in this body that the cavities of the auricles are separated from each other, by a 

 muscular septum, situated internally to that place, which appears contracted 

 externally. These auricles make a muscular production about six lines long, 

 which unites them to the heart, towards the middle and left on its backside. 

 This production is composed of two conduits, separated only by the extension 

 of the septum, which divides the two auricles : it is by these two conduits that 

 the blood flows from the auricles into the heart. The body of these auricles 

 has no adherence to the pericardium, nor any support, except that of the veins, 

 which end in it ; for if you divide these veins, the heart and auricles come out 

 of the body ; and then if you suspend the heart by the auricles, they resemble 

 two funnels joined together, the small end of which opens into the ventricle of 

 the heart, to pour the blood into it : and it is in this manner we are to conceive 

 them, in the natural situation of the animal. 



In order to examine the inside of the heart and its auricles, it must be 

 opened at its inferior surface, supposing the animal turned on its back, because 

 all the orifices either of the arteries or veins, and their valves, are in the op- 

 posite side : therefore a probe may be introduced through one of the arteries 

 into the heart, and so opened upon it ; after that, you cut all this side round 

 about the inferior circumference, from one angle to the other, and then turn 



