•246 THE CHEST. 



a kind of tumour has been formed on the point of it, which has occasionally 

 ulcerated, and proved very difficult to heal. 



The front of the chest is a very important consideration in the structure 

 of the horse. It should be prominent and broad, and full, and the sides of 

 it well occupied. When the breast is narrow, the chest has generally the 

 same appearance ; the animal is flat-sided, 'the proper ca^aty of the chest 

 is less, and the stamina of the horse are materially diniinished, although, 

 perhaps, his speed for short distances may not be affected. When the 

 chest is narrow and the fore legs are too close together, in addition to the 

 want of bottom they will interfere with each other, and there will be 

 wounds on the fetlocks and bruises below the knee. 



A chest too broad is not desirable, but a fleshy and a prominent one ; 

 yet even this, perhaps, may require some explanation. When the fore legs 

 appear to recede and to shelter themselves under the body, there is a 

 faulty position of the fore limbs, a bend or standing over, an unnatural 

 lengthiness about the fore parts of the breast, sadly disadvantageous in 

 progression. 



There is also a posterior appendix to the sternum, which is also 

 cartilaginous. It is called the ensiform cartilage, although it bears little 

 resemblance to a sword. It is flat and flexible, yet strong, and serves as 

 the commencement of the floor or support of the abdomen. It also gives 

 insei'tion to some of the abdominal muscles, and more conveniently than it 

 could have been obtained from the body of the sternum. 



The intercostal Muscles. — The bordei'S of the ribs are anteriorly concave, 

 thin and sharp — posteriorly rounded, and presenting underneath a longi- 

 tiidinal depression or channel, in which run both blood-vessels and nerves. 

 The space between them is occupied by muscular substance firmly attached 

 to the borders of the ribs. These muscles are singularly distributed ; their 

 fibres cross each other in the form of an X. There is a manifest advantage 

 in this. If the fibres ran straight across from rib to rib, they might act 

 powerfully, but their actions would be exceedingly limited. A short 

 m.uscle can contract but a httle way, and only a slight change of form or 

 dimension can be produced. By running diagonally fi'om rib to rib, these 

 muscles are double the length they could otherwise have been. It is a 

 general rule with regard to muscular action, that the power of the muscle 

 depends on its bulk, and the extent of its action on its length. 



The ribs, while they protect the important viscera of the thorax froni 

 injury, are poAverful agents, when acted on by the respiratory muscles, in 

 extending and contracting the chest in the alternate inspiration and 

 expiration of air. In what proportion they discharge the labour of 

 respiration is a disputed question, and into the consideration of which wo 

 cannot enter until something is known of the grand respiratory muscle, the 

 diaphragm. Thus far, however, may be said, that they are inactive in 

 natural respiration, or they certainly act only a secondary part ; but in 

 hurried respiration, and when the demand for arterialised blood is increased 

 by violent exertion, they are valuable and powei-ful auxiliaries. 



This leads to a very important consideration, the most advantageous 

 form of the chest for the proper discharge of the natural or extraordinary 

 functions of the thoracic viscera. The contents of the chest are the lungs 

 and the heart : the first, to render the blood nutrient and stimulating, 

 and to give or restore to it that vitality which wll enable it to support 

 every part of the frame in the discharge of its function, and devoid of 

 which the complicated and beautiful machine is inert and dead ; and the 

 second, to convey tliis purified arterialised blood to every part of the frame. 



In order to produce and to convey to the various parts a sufficient 

 quantity of blood, these organs must be largo. If it amounts not to 



