734 THE CIRCULATORY APPARATUS OF BIRDS. 



is prolonged between the pillars of the diaphragm into the thoracic cavity. Tlie thoracic doct 

 of this animal generally resembles that of the Pig. Yet it sometimes offers in its course and 

 termination very numerous variations; Rudbecky has noticed a bifurcation above the heart, 

 and another bifurcation the branches of wliich anastomose with each other several times. 

 Swammerdam and Steno have figured numerous irregular anastomotic divisions towards the 

 middle of a single canal, to its point of departure. These old authors have indicated and 



Fig. 406. 



THORACIC DUCT OF SMALL RUMINANTS. 



represented double and triple junctions of different forms. Lastly, Bilsius has shown an arch, 

 or rather a very remarkable ring, at the entrance of the vessel, at its junction with the 

 lymphatic vessels of the neck and anterior limbs, and which is more or less analogous to that 

 which I have observed on several occasions in the Horse, Pig, and Cat." • 



CHAPTER III. 



THE CIRCULATORY APPARATUS OP BIRDS. 



We will briefly examine the characteristics of the different portions of the 

 circulatory apparatus — the heart, blood-vessels, and lymphatic vessels — of Birds. 



Article I. — The Heart. 



The heart, in Birds, is situated quite at the entrance to the chest, in the 

 middle line, and is contained in a pericardium that adheres to the posterior 

 diaphragmatic septum and the cervical reservoir. In the domesticated species, 

 it has the form of an acute cone, the base of which is surmounted by a less 

 distinct auricular mass than in the Mammalia. 



Internally it has four cavities. The right ventricle is more crescent-shaped 

 than in Solipeds, and in a manner envelops the left ventricle in front and to the 

 right ; it does not reach the point of the heart. The auricular valve is not 

 tricuspid, and offers a very remarkable arrangement. " This valve, in fact, 

 instead of being formed as usual by membranous curtains, with margin retained 

 by cords fixed to the walls of the ventricles, is composed of a wide muscular leaf 

 which appears to be a portion of the inner wall of the ventricle detached from 

 the interventricular septum. This septum is convex, and the auriculo-ventricular 

 orifice is situated in the space comprised between it and the muscular valve in 

 ' G. Colin, op. cit. 



