ANGIOLOGY 



The Circulatory Apparatus. — The circulatory apparatus consists of 

 two tubular systems: the blood vascular system and the lymphatic 

 system. 



The blood vascular system consists of the heart, the arteries, the 

 veins, and the capillaries. 



The heart is the central, propelling organ. The arteries form a 

 series of efferent tubules, which, by branching, constantly increase 

 in number and decrease in caliber, and which serve to carry the 

 blood from the heart to the tissues. ' The capillaries are extensions 

 from these latter tubules into which the arteries empty, and through 

 the walls of which the interchange of elements between the blood 

 and the other tissues takes place. The veins form a system of 

 converging tubules which receive the blood from the capillaries, 

 decrease in number and increase in size as they approach the heart, 

 and return the blood to that organ. 



The lymphatic system consists of capillaries and veins alone. 

 As in the blood system, the lymph capillaries collect the effete mate- 

 rial and pour it into the lymph veins, and these in turn, carry it to 

 the large blood veins adjacent to the heart. 



Both these systems have one and the same continuous lining, 

 which consists of a single layer of endotheUal cells. In the heart 

 this lining is called the endocardium, and in the vessels, the endo- 

 thelium. It forms a perfectly smooth surface. 



THE HEART (Fig. 21, No. 7) 



The heart of the domestic fowl is located in the median line of 

 the thoracic cavity. It is more anterior and mesial than in mam- 

 mals. Its axis is parallel with the axis of the trunk. The lungs 

 being confined to the dorsal part of the trunk, the lower part of 

 the heart is not surrounded by them, but extends backward, the 

 apex resting in the anterior part of the anterior median fissure of the 

 liver. 



The heart has the form of an acute cone (Fig. 50, No. i), the apex 

 of which is bluntly rounded. 



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