PREPONDERANCE OF FLEXORS. 433 



becomes necessary, therefore, that the neck should be fixed by its 

 extensors, which arise from the lumbar and dorsal regions. By the 

 united action of all these muscles, the deltoid is able to exert its full 

 effect in elevating the humerus. But the deltoid, like other muscles, 

 is capable of acting inversely; as in the case of a person lying on the 

 ground, and attempting to raise himself by laying hold of any object 

 above him. The hand and forearm are thus rendered firm, and the 

 deltoid now contracts from origin to insertion, and, consequently, ele- 

 vates the scapula and clavicle. Again, if a person, in the recumbent 

 posture, endeavours to bend the head forwards, the recti muscles of the 

 abdomen are firmly contracted for the purpose of fixing the sternum, 

 whence the sterno-cleido-mastoidei muscles in part arise, which can 

 then exert their full power in bending the neck forwards. These 

 instances will be sufficient to exemplify the mode in which muscular 

 motions are combined. The same principle prevails over the whole 

 body ; and where a greater number of parts has to be moved, the case 

 must, necessarily, be more complex. 



When a part, movable in various directions, is drawn towards any 

 point, it must be rendered steady, and be prevented from deviating, by 

 the muscles on each side ; and the extent of its motion may be partly 

 regulated by the action of antagonist muscles. Supposing, for instance, 

 that the head is inclined forwards, there must be muscles not only to 

 move it in that direction, but also to prevent it from inclining to the 

 right or left, and to limit the motion forwards ; although doubt may 

 arise, whether this be not entirely effected by the nervous influx sent 

 by volition to the flexors of the head. Hence, some anatomists have 

 considered, that there must, in these cases, be movers, directors, and 

 moderators. 



In sleep, the muscles are perhaps in the most complete state of re- 

 laxation; and, accordingly, this condition has been invoked, as affording 

 evidence of the comparative preponderance of particular antagonizing 

 muscles, flexors and extensors, for example. In perfect sleep, when 

 no volition is exercised over the muscles, the body reposes in a state of 

 semiflexion, which seems to show, that the flexor muscles have slightly 

 the advantage over the extensors. M. Richerand 1 has assigned the fol- 

 lowing reasons for this preponderance. First. The number of flexors is 

 greater than that of extensors. Secondly. The fibres, composing them, 

 are more numerous and longer: take, for example, the sartorius, gra- 

 cilis, semi-tendinosus, semi-membranosus, and biceps, which are flexors 

 of the leg, and the rectus and triceps cruris, which are its extensors. 

 Thirdly. Their insertion is nearer the resistance and farther from the 

 centre of motion, which adds to their force. Fourthly. Their insertion 

 into the bones is at a larger angle, and nearer the perpendicular ; and 

 Fifthly. Their arrangement is such, that the continuation of the move- 

 ment of flexion renders them perpendicular to the bones to be moved. 

 The explanation, afforded by M. Richerand, applies, on the whole, to 

 the case he has selected; but there are many exceptions to it. The 



1 Recueil des Memoires de la Societe Medicate de Paris, an vii. (1799), and Elemens de 

 Physiologic, 13eme edit., par M. Berard, aine; edit. Beige, p. 253, clx., Bruxelles, 1837. 



VOL. i. 28 



