600 TEE ARTERIES. 



on a level with the sixth left intercostal space. The auricular appendages, particularly the 

 right, are more rounded and bulging than in animals. The pulmonary veins, four in number, 

 open on the upper face of the left auricle. 



There are no essential differences to be noted in its internal conformation. We may indi- 

 cate the presence of a fold that passes from the ring of Vieussens to the opening of the inferior 

 vena cava ; this is tlie Eustachian valve. We may also mention the Thebesian valve at the 

 entrance of tlie coronary vein. 



The fibrous rings and muscular fasciculi are disposed as in the Horse. 



The pericardium is a conical sac ; but instead of its base being presented upwards, it rests 

 against the tendinous centre of the diapliragm; its summit is lost among the large vessels; 

 and it adheres to the posterior face of the sternum. 



SECOND SECTION. 

 The Arteries. 



CHAPTER I. 

 GENERAL CONSIDERATIONS. 



Definition. — The centrifugal vessels which carry the blood from the heart to 

 the various organs, are named arteries. 



Division. — These vessels proceed from the heart by two trunks, wluch are 

 perfectly independent in the adult animal ; they originate, one in the right 

 ventricle, the other in the left. 



The first of these trunks — which carries the dark blood — is the pulmonary 

 artery. The second conveys the red blood, and is named the aorta. There 

 exist, therefore, two groups of arteries — the pulmonary system, and the aortic 

 system. 



General Form. — Single at their origin, the two arterial systems soon 

 divide into less voluminous trunks, which again subdivide into successively 

 decreasing canals, until at last their diameter becomes reduced to an extreme 

 degree of tenuity. In a word, the arterial trunks present the ramous disposition 

 of dicotyledonous plants. The total volume of the secondary trunks exceeds 

 that of the primary trunk, and the same relation exists between the respective 

 dimensions of the branches and their ramifications, to the ultimate divisions of 

 the artery. In tracing all the ramifications of one of these systems to a single 

 canal, it will be found that this canal is incessantly increasing, from its origin 

 to its termination, and that it represents a hollow cone with its apex at the 

 heart. ^ 



Particular Form. — Each artery is cylindrical in form, whatever its volume 

 may be. When the diameter of these vessels is measured at their origin and 



' Berryer-Fontaine agaiij discusses this arrangement, and asserts that it is imaginary. 

 According to his calculations, the arterial blood in Man circulates in a cylinder, and not in a 

 cone. The measurements and the calculations we have made with ngard to the arteries of 

 Solipeds, have demonstrated once more that the volume of the terminal branches of an artery 

 Is greater than that of the latter. Consequently, we adhere to the old belief. 



