EIGHTH LECTURE. 



CIRCULATORY AND LYiMPHATIC SYSTEMS, 

 AND THEIR DISEASES AND DISORDERS. 



PART I.— THE CIRCULATORY SYSTEM. 



399. The organs of circulation, in all animals, comprise : — 



I. — The Heart, which, so to speak, pumps blood for 

 purification and circulation. 



2. — The Arteries, which carry blood to various portions of 



the body. 

 3. — The Capillaries, which form the connecting medium 



between arteries and veins. 



4. — The Veins, which return the blood to the heart. 



400. The Heart is a reddish-brown, hollow, cone-shaped muscular 

 organ, situated between the right and left lungs, in the middle of the 

 chest, or thorax (in other words, in the mediastinum), having a base 

 which looks upwards, a body, and an apex pointing downwards in 

 a slightly oblique manner towards the sternum, or breast bone, 

 inclining slightly to the left side. It is composed of involuntary 

 muscular fibres, and is enclosed in a fine fibro-serous sac, or bag, 

 called the peyicavdmm, the surface of the heart being covered by a 

 serous membrane — the epicardium. In the horse and cow it is about 

 eight inches in length from the base to the apex, and weighs from six 

 to seven pounds. The walls on the right side of the heart are much 

 finer and thinner than those on the left, whilst the walls of the left 



