VOL. XXVII.] PHILOSOPHICAL TRANSACTIONS. 603 



large turning, without any support, towards the left side, which gives it the 

 liberty to extend itself when the animal stretches out of its shell, and to refold 

 itself when it retires into it; after that, this artery descends against the back, 

 where it gives some small branches to the spinal marrow; it then returns 

 through the lungs into the abdomen, and here it produces a considerable branch, 

 which divides into two, of which one is distributed to the liver, the stomach, 

 and the intestines, and the other, turning towards the right in the middle of 

 the abdomen, unites to the aorta dextra ; so that these two arteries are only one 

 and the same branch divided into two. This same left aorta continues after- 

 wards to the lower belly, to be distributed to the kidneys, thighs, and the parts 

 below. It is much longer than the right, because of the great circuit it makes 

 on coming out of the heart, to accommodate itself to the motions of the ani- 

 mal, and to make room for its head, which is placed under this artery in the 

 left side, when he draws it into his shell : and it is for this reason that the left 

 branch of the trachea arteria is longer than the right. This artery is also larger 

 than the right aorta, because it furnishes a greater number of parts with blood. 

 It has a distinct orifice into the ventricle of the heart, and has not the least 

 communication with the pulmonary arteries, either in the heart or in any other 

 part. This does not at all resemble the ductus arteriosus in the heart of a 

 human foetus. 



The third artery from the basis of the heart of this animal, is that which I 

 call the right descending aorta : after having pierced the pericardium, it sinks 

 towards the back; then returning through the lungs into the abdomen, where 

 it receives the branch of the left aorta, it is distributed to the right kidney, 

 thighs, bladder, and parts of generation : so that I call these two arteries, the 

 descending aortas, because they distribute the blood to all the inferior parts of 

 this animal, the same as the descending aorta does in all other animals. 



The fourth artery, from the heart, is the ascending aorta. It has an orifice 

 in the ventricle of the heart, common with the right descending aorta: it 

 partly appears under the left aorta coming out of the heart, and ascends in a 

 straight line, till it has pierced the pericardium ; after which it divides into three 

 principal branches, of which the two lateral go to the fore legs, and make the 

 carotid ; the third ascends all along the trachea towards the larynx, and gives 

 branches to all the parts of the neck. 



The disposition of the arteries which go out of the heart being examined ; 

 there only remain the veins, which bring the blood into it from all the parts of 

 the animal. But first it must be observed, that there are no veins which termi- 

 nate in the heart ; for all the veins open into the auricles, which are, as has 



4H 2 



