ANTERIOR EXTREMITY OF THE BODY. 145 



Most authors have advanced the opinion that its width is propor- 

 tionate with that of the chest. In our opinion, it is easy to see in this 

 assertion the false interpretation of the fact (for the most part very well 

 established) that narrowness of the breast accompanies a thorax of 

 little capacity and slender limbs. 



It might be supposed, indeed, that there ought to be a certain 

 relation between this narrowness and the space enclosed by the first two 

 ribs. This is, however, an error which we have exposed by more than 

 fifty observations made upon the living subject and completed after- 

 wards upon the cadaver. We have never found marked differences in 

 this respect among subjects of the same size, whatever may have been 

 the width of the breast. This is due to the simple reason : it is not 

 at the anterior extremity that the dimensions of the chest vary, but 

 rather in the middle and posterior regions. Also, the differences in the 

 width of the pectoral region are the result of causes other than the 

 separation of the anterior ribs. We must attribute them to the varying 

 thickness of the pectoral muscles which form its base. It is also true 

 that -this region can accidentally become narrow in animals whose 

 thorax is spacious. It is only necessary to place them in bad hygienic 

 conditions, or to give them improper food and injudiciously-chosen work, 

 to convince ourselves that emaciation causes a diminution of its width. 



It is physiologically true, however, that the general development of 

 the respiratory apparatus is directly proportional to that of the muscular 

 system. The functional activity of the muscles causes an augmenta- 

 tion of their volume, and their contractions produce an increase of the 

 amount of oxygen consumed. No lungs, no muscles ; and, conversely, 

 dense and vigorous muscles require a spacious thorax ; whence it follows 

 that the width of the pectoral region, owing to the volume of its muscles, 

 should coincide with a certain degree of respiratory power. If, there- 

 fore, this region is narrow, it becomes desirable to determine to what 

 cause this narrowness is due, whether to that of the thorax directly, or 

 to the animal's " condition." 



The size being equal, the breast of the English thoroughbred 

 horse is less wide than that of the heavy coach-horse, whilst he is 

 endowed with a chest equally if not more spacious. In this case the 

 harmonious development of the locomotory apparatus must also be 

 considered ; the power of the muscles, instead of being the effect of 

 their thickness, is due to their length ; and the sternum appears more 

 prominent than it does in a horse with thick muscles. Besides, these 

 muscles are dense, firm, and habituated to repeated energetic and 

 extensive contractions. 



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