THE CHEST. 169 



The point of the breast-bone may be occasionally injured by blows, or by the pres- 

 sure of the collar. It has been, by brutal violence, completely broken off from the 

 sternum ; but oftener, and that from some cruel usage, 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 cavity of the chest is diminished, and the stamina of the horse are 

 materially diminished, 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 ensifnrm 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 insertion 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 borders of the ribs are anteriorly concave, thin and 

 sharp posteriorly rounded, and presenting underneath a longitudinal 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 action would be exceedingly limited. A 

 short muscle can contract but a little way, and only a slight change of form or dimen- 

 sion can be produced. By running diagonally from 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 from injury, are 

 powerful agents 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 we cannot enter, until 

 something is known of the grand respiratory muscle the diaphragm. Thus far, 

 however, may be said, that they are not inactive in natural respiration, although 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 powerful 

 auxiliaries. 



This leads to a very important consideration, the most advantageous form of tnrs 

 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 will 

 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 this purified arterialised blood to every part of the frame. 



In order to produce, and to convey to the various parts, a sufficient quantity oi 

 blood, these organs must be large. If it amounts not to hypertrophy, the larger thi> 

 heart and the larger the lungs, the more rapid the process cf nutrition, and the moro 

 perfect the discharge of every animal function. 



Then it might be imagined that, as a circle is a figure which contains more than 

 any other of equal girth and admeasurement, a circular form of the chest would bf 

 most advantageous. Not exactly so; for the contents of the chest are alternately 

 expanding and contracting. The circular chest could not expand, but every change 

 of fora, woul d be a diminution of capacity. 



That form ^f chest which appr; xches nearest to a circle, wb ; ,le it admits of r^fficiei* 

 15 w 



