CHAPTER X 



THE BLOOD VASCULAR SYSTEM, AND THE LYMPH VASCULAR 



SYSTEM 



BLOOD VASCULAR SYSTEM 



The blood is the internal medium on which the tissues live. 

 It is carried through the body by branched tubes named 

 blood-vessels. It is driven along these tubes by the action of the 

 heart, which is a hollow muscular organ placed in the centre of 

 the vascular system. One set of vessels — the arteries — conducts 

 the blood out from the heart and distributes it to the different 

 parts of the body, whilst other vessels — the veins — bring it 

 back to the heart again. The blood from the arteries gets into the 

 veins by passing through a network of fine tubes which connect 

 the two, and which are named, on account of their small size, the 

 capillary {i.e. hair-like) vessels. 



Blood Vascular 

 System 



f Heart. 



Arteries — small arteries are named arterioles. 



Capillaries. 

 . Veins — small veins are named venules. 



We shall see that the structure of these several parts is adapted 

 to their respective uses. 



HEART 



The heart is a hollow, muscular organ, situated in the thorax 

 between the lungs, behind the sternum, and above the central 

 depression of the diaphragm. It is about the size of the closed 

 fist, shaped like a blunt cone, and so suspended by the great 

 vessels that the broader end or base is directed upward, back- 

 ward, and to the right. The pointed end or apex points down- 

 ward, forward, and to the left. The impulse of the heart 

 against the chest wall is felt in the space between the fifth and 

 sixth ribs, a little below and to the inner side of the left nipple. 

 M 161 



