276 BUREAU OF ANIMAL INDUSTRY. 



It was the j^rcat Bacon Avho wrote: "The human body may he com- 

 pared, from its complex and delicate organization, to a musical instru- 

 ment of the most perfect construction, but exceedingly liable to 

 derangement." In its degree the remark is equally applicable to the 

 equine bod}', and if we would keep it in tune and profit by its har- 

 monious action we must at least acquaint ourselves with the relations 

 of its parts and the mode of their cooperation. 



The bones, then, are the hard organs which in their connection and 

 totality constitute the skeleton of an animal. They are of various 

 forms, three of which — the long, the flat, and the small — arc recog- 

 nized in the extremities. These are more or less regular in their form, 

 but present upon their surfaces a variety of aspects, exhibiting in 

 turn, according to the requirement of each case, a roughened or smooth 

 surface, variousl}^ marked with grooves, crests, eminences, and depres- 

 sions, for the necessary muscular attachments, and, as before men- 

 tioned, are connected b}^ articulations and joints, of wdiich some are 

 immo\able and others of a movable kind. 



The substance of the bones is composed of a mass of combined 

 earthy and animal matter, surrounded by a fine, fibrous enveloping 

 membrane (the periosteum) which is intimately adherent to the external 

 surface of the bone, and is, in fact, the secreting membrane of the 

 bony structure. The bony tissue proper is of two consistencies, the 

 external, portion being hard and "compact," and called by the latter 

 term, while the internal, known as the "spongy," or "areolar tissue," 

 corresponds with these descriptive terms. Those of the bones which 

 possess this latter consistency contain also, in their spongy portion, 

 the medullary substance known as marroio, which is deposited in large 

 quantities in the interior of the long bones, and especially where a 

 central cavity exists, called, for that reason, the medullary cavity. 

 The nourishment of the bones is eft'ected by means of what is known 

 as the nutrient foramen^ an opening established for the passage of the 

 blood vessels which convey the necessary nourishment to the interior 

 of the organ. There are other minutire concerning the nourishment of 

 the skeleton, such as the venous arrangement and the classification 

 of their arterial vessels into several orders, which, though of interest 

 as an abstract stud}', are not of sufficient practical value to refer to 

 here. 



The active organs of locomotion, the vuiscles, form, speaking gen- 

 erally, the fleshy covering of the external part of the skeleton and 

 surround the bones of the extremities. They var}' greatly in shape and 

 size, being flat, triangular, long, short, or broad, and are variously 

 and capriciously named, some from their shape, some from their situa- 

 tion, and others from their use, and thus we have abductors and adduc- 



