300 DISEASES OF THE IIOESE. 



the theme as a practical collation of facts to be remembered, analyzed, 

 ai^plied, and utilized. 



It was the great Bacon vvho Avrote : " The human body may be 

 compared, from its complex and delicate organization, to a musical 

 instrument of the most perfect construction, but exceedingly liable 

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

 the equine body, and if we would keep it in tune and profit by its 

 harmonious action we must at least acquaint ourselves w^ith the rela- 

 tions of its parts and the mode of their cooperation. 



ANATOMY. 



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

 totality constitute the skeleton of an animal (see Plate XXIII). 

 They are of various forms, three of which — the long, the flat, and the 

 small — are recognized 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, variously marked with grooves, 

 crests, eminences, and depressions, for the necessary muscular attach- 

 ments, and, as before mentioned, are connected by articulations and 

 joints, of which some are im.movable and ethers movable. 



The substance of the bone is composed cf 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 consisten- 

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

 the latter term, while the internal, known as the " spongy " or " areo- 

 lar tissue," corresponds to the descriptive terms. Those of the bones 

 that possess this latter consistency contain also, in their spongy por- 

 tion, the medullary substance known as marrow, 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 effected by means of what 

 is known as the nutrient foramen, an opening established for the 

 passage of the blood vessels which convey the nourishment necessary 

 to the interior of the organ. Concerning the nourishment of the 

 skeleton, there are other minutiae, such as the venous arrangement 

 and the classification of their arterial vessels into several orders, 

 Avhich, though of interest as an abstract study, are not of sufficient 

 practical A-alue to refer to here. 



The active organs of locomotion, the muscles (see Plate XXIII), 

 speaking generally, form the fleshy covering of the external part of 

 the skeleton and surround the bones of the extremities. They vary 



