228 



diagonally or obliquely round the vessel. In this coat the nutrient 

 vessels, the vasa vasorum, form a capillary net-work, from which a 

 few penetrate as far as the muscular coat. 



The veins differ from arteries in possessing thinner walls, less elas- 

 tic and muscular tissue, and for the most part a stronger tunica adven- 

 titia. Thej^ collapse when cut across or Avhen they are empty. The 

 majority of A^eins are provided with A^alves; these are folds of the lin- 

 ing membrane, strengthened by fibrous tissue. They favor the course 

 of the blood and jirevent its reflux. The nerves which supply both 

 the arteries and the veins come from the sympathetic system. The 

 smaller arteries terminate in the system of minute vessels, known as 

 the capillaries, which are interjjosed between the termination of the 

 arteries and the commencement of the veins. Their average diame- 

 ter is about one three-thousandth of an inch. 



SOUNDS OF THE HEART. 



By placing the ear behind the elbow against the left side of the 

 chest two distinct sounds can be heard at each heart-b<*at in health. 

 The first is rather mufiled and prolonged, the second is short and 

 sudden. The first is caused by the contraction of the A^entricles, the 

 closing of the auriculo-ventricular valves, and the forcible propulsion 

 of the blood into the arteries; the second follows immediately, and is 

 due to the reflux of the blood just forced into the arteries, and the 

 sudden closure of the valves Avhich prevent its return to the heart. 

 In disease of the heart or valves these sounds are generally modified, 

 or supplanted by others, which vary so much in character and are so 

 difficult to describe that we can not consider them here; long and 

 extensive experience is required to distinguish them i:>ractically. 



CHARACTERS OF THE PULSE. 



The circulation of the blood through the heart is constant, and is 

 maintained by the propelling activitj^ of this organ. In the horse the 

 heart beats from thirty-six to forty-six times a minute, varying with 

 the disposition, breed, and temperament of the animal. In the foal 

 the pulse is about three times as rapid as in the adult, from six months 

 to a year about twice as quick, and in the two-year-old about one- 

 quarter faster. The pulse is usually taken at the angle of the jaw, 

 where the artery crosses the bone, and its force or character is often 

 indicative of the nature of the disease from which an animal may be 

 suffering. The jiulse, therefore, is named in accordance with its char- 

 acter as slow, soft, small, full, weak, quick, hard, irregular, intermit- 

 tent, venous, etc. 



Slow pulse is one where the number of beats is less than normal, 

 and is often found in certain diseases of the brain. 



Soft or cornpressihJe pidse is one Avhere the beat is rather weak, but 

 not abnornuilly rapid. It is often found in debility due to want of 



