164 LOCOMOTION, [CHAP. vn. 



for all these muscular fibres to be attached to the tendinous ones on 

 the same level, on account of the great difference in bulk between 

 the two structures. Hence, in such cases, we find the muscular 

 fibres to end in tendon in regular progression one after the other, 

 and the tendon at its muscular extremity to be expanded, some of 

 its fibres being long, others short. And yet the inconvenience 

 which would ensue from the muscular fibres being of unequal length 

 in the same organ is counteracted by the tendon at their other ex- 

 tremity having its fibres precisely reversed ; as in the rectus of the 

 thigh, and numerous other instances. "Where muscular fibres are 

 really of different lengths in a muscle, it is because, from the direc- 

 tion in which they act, they have to shorten to different degrees. 

 Thus, in the square pronator of the fore-arm, the deeper and shorter 

 fibres are attached to apart of the radius, which in pronation passes 

 through a much smaller space than that to which the superficial 

 and longer fibres are fixed : and under the innumerable modifica- 

 tions of muscular form in man and animals, however force is sacri- 

 ficed to mechanical exigencies, or other causes, it is invariably 

 accomplished with the utmost ceconomy of power consistently with 

 the end in view ; there is never any waste, never any force provided 

 which is not wanted. 



Where a great mass of fibrous tissue runs into a muscle, the num- 

 ber and obliquity of the muscular fibres are very much increased, 

 while the length of each is diminished ; and, as a general result, 

 the power of such a muscle is great, the extent of its contractions 

 comparatively limited. 



A given mass of contractile material may be arranged as a few 

 long fibres (as in the sartorius), or as many short ones (as in the 

 masseter) : its contractions would, in the former case, be charac- 

 terized by their extent ; in the latter, by their power ; for, cceteris 

 paribus, the extent is as the length, the power as the thickness. 



The terms origin and insertion are employed with great conve- 

 nience in ordinary language, to denote the more fixed and the more 

 moveable attachments of muscles. In human anatomy general con- 

 sent has sanctioned their use, and even with few exceptions their 

 particular application to each muscle in the body ; although this 

 assignment is in many cases arbitrary, in consequence of its being 

 impossible to determine which attachment is the more frequently 

 the fixed one. 



The arrangement of the fibres in the heart is very peculiar. 

 Without attempting a particular account of their course, we may 

 state that they do not preserve the same parallelism, nor extenc 



