■ in the Ftetus of Vertebrated Antmals. S73 



established by the observations previously related, that, 1st, this 

 organ consists at first, in all vertebrated animals, of a simple 

 membranous tube, forming a continuation, and connected with 

 the venous ind arterial Vessels, 2d, This tube of the heart iiJ 

 invariably situated on the lower and anterior side of the cesopha. 

 gus. 3d, The blood at first enters this tube towards its posterior 

 extremity, and on the left side of the body, and issues at the an- 

 terior extremity, and towards the right side. 4th, The changes 

 which the tube undergoes in its gradual conversion into the heart 

 of the adult, are, to a certain extent, the same,orat least analogous, 

 in all the orders of vertebrata. 5th, The auricle and bulb of the 

 aorta are separated from the ventricle by a constriction in the 

 paries of the tube. 6th, A curvature takes place in the tube, so as 

 to bring together its two extremities, or to make the auricle and 

 bulb of the aorta approach one another ; this curvature being 

 such, that the auricle is always situated behind, or rather above 

 the ventricles. 7th, In fishes and batrachia, the form of the heart 

 is perfected, the ventricle becomes very thick and muscular, the 

 auricle is dilated, and valves are formed near the apertures, while 

 this organ remains simple and undivided, or while the blood 

 which enters it is propelled through a single vessel. iL vh. In lizards, 

 serpents, and turtles, while the same or analogous changes take 

 place in the general structure of the heart, in the strength and 

 thickness of its parietes, or in the relative position of its parts, the 

 cavities of this organ are more or less completely divided, so as to 

 separate the blood which passes through it into more than one 

 stream ; the auricle being divided by the formation of a sep- 

 tum advancing from above downwards, the ventricle, by a parti- 

 tion which rises from the apex towards the base. 9th, The heart 

 of birds and mammalia is seen to undergo the same subdivision, 

 and the right and left cavities communicate for some period of 

 fcctal life with one another ; but, in these animals, the partitions 

 by which the auricles and ventricles are separated become com- 

 plete, and no longer leave any opening from the cavities on one 

 side of the heart into those of the other. 10th, In mammalia, the 

 growth of the septum, in the interior of the ventricle, is accom- 

 panied by the formation of a notch or constriction on the out- 

 side, by which the apex of the heart is rendered double for a 

 time. 11th; At the same time, in the higher reptiles, birds, and 



