Book VII. PHYSIOLOGY OF THE HORSE. 897 



mechanism, we need only turn our attention to the contra-disposition of these angles in 

 the fore and hinder supporting pillars. Had these angles presented themselves in the 

 same direction, the body must have been precipitated forward or backward ; but each 

 offering a counteraction to the other, the body is firmly sustained within them. 



5662. The bony masses are operated on by viuscles, for tliis deviation from a perpendi- 

 cular direction in the various bony portions of the limbs, must necessarily have powers 

 to correct it, which is done by the muscles ; and wherever the angles are found most 

 extensive, the muscles will be found proportionally strong and large. This muscular 

 exertion, to counterbalance the angular inclination, occasions fatigue ; as the set of 

 muscles immediately employed becoming weary, the animal is obliged to call another set 

 into action, which change is necessarily more or less frequent as the animal is weaker 

 or stronger. 



5663. The extent of the action of the bony portions of the extremities, is the produce 

 of the length and direction of the various parts entering their composition, and of the 

 different angles they are capable of forming, as progression itself is effected by these 

 angles closing, and suddenly extending themselves again. The force of the action arises 

 from the direction of the component parts of the^ngles, in combination with the agency 

 of the muscles. The repetition of the action is dependant on the muscles alone ; but as 

 the original action arose out of the length and direction of the parts, so it will be evi- 

 dent that fn every subsequent repetition, it will be more or less extensive, as these are 

 more or less perfect in their formation, even though the muscular exertions shoidd be 

 the same : thus some strong animals cannot move so fast as others with less strength, as 

 the cart-horse and racer, or greyhound and mastiff*. 



5664. The bony mechanism of the fore and hinder extremities presents some differences. 

 That of the fore limb may be said to exhibit altogether a different character. The 

 fore-leg bones are much less angular, and appear framed purposely to receive the weight 

 imposed on them by the impulse of the hinder limbs. This weight they are destined to 

 sustain, until the elevation is forced on them by the tendency the general inclined mass 

 has to meet the ground, or to find its common centre in the earth. The fore extremi- 

 ties, under this view of the matter, could not have been placed with equal wisdom in 

 any other situation, nor have taken any other form. The hinder extremities having 

 less weight on them, and at no time bearing an increase of pressure as the fore do, by 

 the impetus communicated from behind, are much more angular ; and their angles, by 

 being thrown into a backward direction, affbrd the necessary impetus for the projec- 

 tion of the body forward. This important operation of impelling the mass being almost 

 wholly dependent on the hind extremities, as that of sustaining it is principally con- 

 fined to the fore extremities ; so the former are also much stronger in point of mus- 

 cular apparatus; by which their angles can be advantageously opened and closed with 

 superior effect in progression. 



5665. The appendages to bone are cartilage or gristle, periosteum, medulla or marrow, ligaments, and 

 synovia or joint oil. Cartilages are of three kinds, articular (1850.) which cover the ends of th^ bones by 

 a thin layer, enabling them to'slide easily on one another ; nonarticular, or such as are placed between 

 bones immovably joined ; unattached, as those of the ears and larynx; and temporary, as the ends of 

 bones in very young animals before their earthy deposit is completed. The general nature of cartilage is 

 smooth, white, solid, elastic, and hard. TUhe periosteum is a general uniting membrane to bones and their 

 appendages (1845.), on i^ the skull, called pericranium; when it covers ligaments, peridesmium ; and 

 perichondrium when it invests cartilage. Its uses appear to be to furnish vessels to the bones. It is 

 little sensililc, except under inflammation, when it becomes highly so. Medulla, or marrow, is a soft fatty 

 substance deposited in the cavities of bones. 



5666. Ligaments (1854.) are close, compact, fibrous substances, of immense strength in the horse, 

 necessary to bones as a connecting medium ; ligament is also a common membrane in every part of the 

 body. The nature of ligament is considered as inelastic ; there are, however, many exceptions, of which 

 the cervical and metacarpal and metatarsals are instances. In some cases they are semicartilaginous. 

 The suspensory ligaments attach and suspend parts, as that of the thigh bone to its socket, &c. Capsular 

 ligaments surround the two opposed ends of jointed bones, and form a complete cavity. 



5667. The synovia or joint oil, being secreted from the inner surface of the capsular ligaments, fills up 

 this cavity, and aftbrds a slippery medium, which enables the bones to slide readily over each other. 



5668. Muscle is that part of the body of the horse which we term flesh, to distinguish it from skin, 

 gristle, bone, ligament, &c, ; and the phenomena it exhibits, are so universal, that we are warranted in 

 considering that it exists in every animal. Muscles appear composed of bundles of reddish fibres, the 

 ultimate division of which it is impossible to trace. When a number of these fibres are connected together 

 into a determinate form and circumscribed extent, it is called a muscle ; and as the motions of an animal 

 are very various, and as almost all motion is operated through the agency of the muscles ; so the peculiar 

 shape they take on is very varied. Muscular fibre is spread over the body, and it has been very properly 

 remarked, that our ideas of it are probably too limited : thus it constitutes a principal part of all the 

 viscera, and enters, it is probable, into the composition of many membranes. But what is more generally 

 considered as a muscle, is a distinct body having its determinate parts. To the generality of muscles, 

 particularly to those ending in bones, is added a portion of a very different nature, called tendon. 



5669. Tendons are insensible, inelastic, tough, fibrous substances, of a whitish colour : expanded into 

 thin layers, they are called aponeuroses. The tendons are eminently useful to muscles, for the size of 

 the termination is thereby diminshed, without the strength ibeing decreased. What would have become 

 of the lightsome elegant limb, had their large muscular masses been continued downwards of the di- 

 mensions we witness them above in the shoulder and thigh, instead of the condensed substance of the 

 tendons or back, and fore sinews? Muscles are highly vascular, as their color testifies ; but the tendons 

 are very little so, hence their powers of life are very different : one can regenerate itself with ease, the 

 other with extreme difficulty. The muscles also possess a large .share of nerves, and consequently of 

 sensibility and irritability, to which properties the surprising phenomena they exhibit must be attri- 



3 M 



