PECULIARITIES OF THE FffiTtfS. 271 



organs of circulation, with the mother. Its peculiarities, there- 

 fore, may be studied under two heads: those which arise from 

 the want of respiration, and those which are required for its 

 nourishment. The peculiarities of the first order are se 

 in the-thorax, and those of the second in the abdomen. 



SECT. I. OF THE PECULIARITIES OF THE FO3TUS, ARISING FROM THE 



WANT OF RESPIRATION. 



The Heart, at a very short period after conception, so early 

 as about the end of the first month, is sufficiently developed to 

 be in a state of great activity. The first indication of its exist- 

 ence, and, indeed, of the life of the new animal, is a small tre- 

 mulous point, called the Punctum Saliens, from its incessant 

 motion. The muscular structure of it is soon evolved, and 

 in a few weeks becomes very manifest. At the earliest visible 

 period of the heart in the incubated egg, which affords a satis- 

 factory analogy, it consists of two vesicles united by a canal, 

 (Canalis Auricularis of Haller.) One of the vesicles is the right 

 auricle; the other is the left ventricle, and is probably the first 

 to pulsate. The aorta is also visible, as well as the venae cavae. 

 The circulation, at this period, is very simple : the blood, start- 

 ing from the left ventricle, is propelled into the aorta; it is col- 

 lected from the ramifications of the last into the two venae cavag, 

 and thereby brought to the right auricle; it is then propelled by 

 the right auricle through the canalis auricularis into the left 

 ventricle, whereby its round is completed, and it then starts 

 again. This is the most simple kind of circulation, and is found, 

 in fact, during the whole lives of such animals as do not breathe 

 by lungs; for example, fish. As the gills in them take the place 

 of lungs, a branch from the aorta, spent upon the gills, is suffi- 

 cient for their purposes of respiration. 



The terms right auricle and left ventricle have been used, be- 

 cause the cavities alluded to perform the functions of the adult 

 state; but in the progress of the development of the heart, a par- 

 tition begins to show itself which ultimately divides each of them 

 into two distinct compartments, whereby we have a right auri- 

 cle and a left one, a left ventricle and a right one. And the 

 canalis auricularis is reduced from a canal into a short orifice, 



