MUSCULAR MOTION. 113 



nent and perceptible they are to the grasp of the finger and thumb, 

 the " better" in kind we reckon them to be ; and it is, perhaps, as 

 good a criterion of their quality as we can have, that they " stand 

 out well" from the cannon bone, feel tense, and hard, and clean, and 

 perceptibly distinct from another cord, between them and the bone, 

 the suspensory ligament, and that the leg altogether, below the 

 knee, measures much in breadth and much in circumference. 



MUSCULAR MOTION. 



The property possessed by an animal body of locomotion — self- 

 movement — is of a nature altogether different from any we witness 

 in machinery: how ingenious soever a piece of mechanism may be, 

 and imitative of the movements of the vital machine, there is still 

 this essential difference between them — that one moves through an 

 extrinsic force or power communicated to it ; whereas, in the other, 

 the power of motion is created or generated. It is, in the strictest 

 sense of the words, a self-moving machine, the other being but 

 self-moved : and in the muscles reside the source of motion. 

 They, during life, possess power of contracting or shortening 

 their lengths, through which simple change all the movements 

 of the body are brought about. What it is that enables them to 

 contract, what alterations of structure or arrangement they undergo 

 during contraction, is a question that has puzzled those who have 

 made themselves best acquainted with their intimate texture and 

 organization. We must, therefore, content ourselves with a know- 

 ledge of the established facts, that the self-moving power resides 

 in the muscles, and is dependent on their vitality ; dead muscle, 

 or flesh, being devoid of any such property. 



The contraction of a muscle has the effect of bringing nearer 

 together the parts to which its ends or extremities are attached ; 

 either both attachments move in approximation, or, one being fixed, 

 the other moves towards it. The tail, e. g. (which is a good ex- 

 emplification of muscular action), is raised by the contraction of 

 muscles running from the croup to its upper surface, called, from 

 their office, the erector es coccygis ; and is depressed by muscles 

 running underneath, from within the pelvis to its under surface, 



Q 



