MUSCULAR MOTION. 115 



practical horsemen full well know, that, to raise the tail of a strong- 

 docked horse, requires often more than the strength of the strongest 

 man's arm. Horse-dealers and grooms, indeed, and connoisseurs 

 in horses, often take the strength of the dock (of the tail) as an 

 estimate of the general muscular powers of the animal ; and the 

 criterion is one by no means to be despised, it being but reasonable 

 to infer that great strength in one part would not be unattended 

 with correspondent power in others. 



The limbs of the horse furnish us with beautiful illustrations of 

 the force and velocity, extent and variety, of muscular motion. 

 In the fore-limb no less than thirty muscles are employed; eighteen 

 being occupied in the movements of the shoulder and arm, the 

 remaining twelve with those of the leg and foot. When speaking 

 of the bones composing these parts, I said that between the shoul- 

 ders the fore-quarters of the body were in a manner suspended 

 through the medium of attaching muscles. There is one muscle 

 especially designed for the performance of this function — the ser- 

 ratus magnus — a muscle of vast magnitude and power, which, 

 though by anatomists regarded but as one, might with just reason, 

 by the physiologist, be described as many ; inasmuch as by such a 

 supposition alone can he account for its unwearied discharge of the 

 laborious duties assigned it. Its twelve distinct origins from the 

 cervical vertebrse and ribs ought to be considered as twelve distinct 

 portions of it ; some of which are in continual action, while the 

 others are recruiting their tone by repose. Another important duty 

 performed by this muscle, and one in which it is probable most if 

 not all of its divisions are engaged, is that of, during the action of 

 the fore-limbs, fixing the central part of the scapula to the ribs 

 while its upper and lower ends revolve, in segments of circles, 

 backwards and forwards ; the other muscles attaching the scapula 

 to the trunk being employed in effecting the revolving movements. 



With the exception of the joint at the shoulder, between the sca- 

 pula and humerus, the joints of the fore-limb are so constructed that 

 they can hardly be said to admit of any motions beyond those of 

 flexion and extension ; and therefore a very proper division of the 

 muscles moving them has been made into fexors and extensors. 

 It might be imagined that one or two of each sort would be all that 

 was required for such simple movements ; when, however, it is 



