428 



MUSCULAR MOTION. 



Fig. 181. it ; and the course of the mus- 



cle would have been so modi- 

 fied as to convert the conve- 

 nient and symmetrical mem- 

 ber into a cumbrous, webbed 

 instrument, badly adapted for 

 the multitudinous purposes to 

 which it has to be applied. 



The same effect results, as 

 Sir Charles Bell 1 has remark- 

 ed, from the course of ten- 

 dons and their confinement by 

 sheaths, strengthened by liga- 

 ments. If the tendon A, Fig. 

 181, took the shortest course 

 to its termination at B, it 



would draw up the toe with more force ; but the toe would lose its 



velocity of movement. 



To favour this velocity, we find that the majority of muscles are in- 

 serted obliquely into 



Fig. 182. 



f~^ 'C^ ~W f 



\jr _lli J~|_ 



iimiminirR 



Tendon of the Great Toe. 



their levers, and the 

 fibres into the ten- 

 dons. By this ar- 



Action of Intercostal Muscles. 



rangement, as we 

 have proved, consi- 

 derable loss of power 

 results; but in the 

 majority of cases, 

 the motion is effected 

 by a less degree of 

 decurtation than if 

 the muscles were straight. Let A B and C D, Figs. 182 and 183, be 

 parts of two ribs that are parallel, and continue parallel till brought 

 into contact by the action of the straight muscle E F ; or by that of the 

 oblique muscles F Gr and F H. Now it is obvious, that when the point 



E comes in contact 



Fi s- 183 - with F, the length 



of the straight mus- 

 cle E F must be 

 null; whilst that of 

 the oblique muscles 

 will only have expe- 

 rienced a decurta- 

 tion equal to Gr g 

 and H A, Fig. 182 ; 

 and to F g and F h, 

 Fig. 183. It is 

 clear, also, that, in these cases, the straight muscles can never so con- 



J.-1. 



Action of Intercostal Muscles. 



Animal Mechanics, Library of Useful Knowledge, p. 27, Lond., 1829. 



