170 THE HORSE. 



The breast-bone is in the colt composed of six bones, which in the full, 

 grown horse unite into one. Seven or eight of the ribs, the number occa- 

 sionally varying, are attached to the sternum by very strong ligaments. 

 These are called the true ribs, and they increase in length from the first to 

 the seventh. The remaining ten or eleven are called false ribs ; they 

 become gradually shorter, and narrower, and rounder; and their direction 

 is more backward, in order to increase the cavity of the thorax and belly, 

 and to strengthen the roof of the belly. Their cartilages are not attached 

 to the breast-bone, but to each other, and yet connected with the breast- 

 bone, and sharing in all its motions by means of the cartilage of the last 

 true rib, with which they all unite. In consequence of these shorter ribs, 

 with long elastic cartilages, the bulk of the chest and of the belly is mate- 

 rially increased, and the ribs are much more easily moved. 



Between the ribs, and mainly contributing to their motion, are two 

 layers of muscles, the intercostals (between the ribs). According as the 

 ribs are brought nearer to, or recede from each other, the cavity of the 

 chest will be increased or diminished. These two layers are curiously 

 contrived. If the fibres ran straight across from rib to rib, they would be 

 exceedingly short ; a short muscle could have but little contraction, and 

 a very slight change of form or dimension could be produced. They 

 run diagonally from rib to rib, and thus are more than double the length 

 that they could otherwise have been j and so the degree of contraction is 

 doubled, and the ribs are moved through a greater space. More perfectly 

 to produce this effect, the muscular fibres of the outer layer run one way, 

 and those of the inner layer a contrary, crossing each other in the form of 

 an X. When these muscles contract, as they act from the fore ribs upon 

 the hinder ones, although the ribs are brought nearer to each other, they 

 are thrown outward, and the real effect is to expand, and not to contract 

 the cavity of the chest. This is, perhaps, somewhat difficult to imagine, 

 but it is the actual explanation of the matter. The ribs are drawn power- 

 fully forward, and when drawn forward, they must be thrown outward, and 

 the chest is necessarily expanded. 



MUSCLES OF THE BREAST. 



Of the proper form of the trunk we have already spoken. There are 

 some important muscles attached to the breast, and therefore, every horse 

 should have a breast tolerably expanded. In the cut, page 154, and in that 

 at page 168, are seen a very important pair of muscles, the pector ales trans - 

 versi, or pectoral muscles, forming two prominences in the front of the chest, 

 and extending backward between the legs. They come from the fore and 

 upper part of the breast-bone ; go across the inward part of the arm, and 

 reach from the elbow almost down to the knee. They confine the arm to 

 I he side in the rapid motion of the horse, and prevent him from being, 

 what horsemen would call, and what is seen in a horse pushed beyond his 

 /latural power, " all abroad." Other muscles, pectorales magni et parv', 

 the great and little pectorals, rather above but behind these, go from the 

 breast-bone to the arm, to draw back the point of the shoulder, and 

 bring the shoulder upright. Another and smaller muscle goes from the 

 breast-bone to the shoulder, to assist in the same ofiice. A horse, there- 

 fore, thin and narrow in the breast, must be deficient in important muscular 

 power. 



Between the legs and along the breast-bone is the proper place in v hich 

 to insert rowels, in cases of inflamed lungs. 



