FORM AND ATTACHMENT OF MUSCLES 359 



the Rectus abdominis, Obliquus capitis, Transversalis; (3) from their uses, as 

 Flexors, Extensors, Abductors, Levators, Compressors, etc.; (4) from their shape, 

 as the Deltoid, Trapezius, Rhomboideus, Digastric; (5) from the number of their 

 divisions, as the Biceps, the Triceps; (6) from their points of attachment, as the 

 Sternomastoid, Sternohyoid, Sternothyroid. 



In the description of a muscle the term origin is meant to imply its more fixed 

 or central attachment, and the term insertion, the movable point to which the 

 force of the muscle is directed; but the origin is absolutely fixed in only a verv 

 small number of muscles, such as those of the face, which are attached by one 

 extremity to the bone and by the movable integument; the greater number of 

 muscles can be made to act from either extremity. 



In the dissection of the muscles, the student should pay especial attention to 

 the exact origin, insertion, and actions of each, and its more important relations 

 with surrounding parts. While accurate knowledge of the points of attachment of 

 the muscles is of great importance in the determination of their actions, it is not to 

 be regarded as conclusive. The action of a muscle deduced from its attachments, 

 or even by pulling on it in the dead subject is not necessarily its action in the 

 living. By pulling, for example, on the Brachioradialis in the cadaver the hand 

 may be slightly supinated 1 when in the prone position and slightly pronated when 

 in the supine position, but there is no evidence that these actions are performed 

 by the muscle during life. It is impossible for an individual to throw into action 

 any one muscle; in other words, movements, not muscles, are represented in the 

 central nerve system. To carry out a movement a definite combination of muscles 

 is called into play, and the individual has no power either to leave out a muscle 

 from this combination, or to add one to it. One muscle (or more) of the combina- 

 tion is the chief moving force; when this muscle passes over more than one joint 

 other muscles (synergic muscles) come into play to inhibit the movements not 

 required; a third set of muscles (fixation muscles) fix the limb i. e., in the case 

 of the limb movements and also prevent disturbances of the equilibrium of 

 the body generally. As an example, the movement of the closing of the fist 

 may be considered: (1) The prime movers are the Flexores digitorum, Flexor 

 longus pollicis, and the small muscles of the thumb; ('2) the~syrrergic muscles are 

 the Extensores carpi, which prevent flexion of the wrist; while (3) the fixation 

 muscles are the Biceps and Triceps, which steady the elbow and shoulder. A 

 further point which must be borne in mind in considering the actions of muscles 

 is that in certain positions a movement can be effected by gravity, and in such a 

 case the muscles acting are the antagonists of those which might be supposed 

 to be in action. Thus, in flexing the trunk when no resistance is interposed the 

 Erectores spinae contract to regulate the action of gravity, and the Recti abdominis 

 are relaxed. 2 



By a consideration of the action of the muscles the surgeon is able to explain 

 the causes of displacement in various forms of fracture, and the causes which 

 produce distortion in various deformities, and, consequently, to adopt appro- 

 priate treatment in each case. The relations, also, of some of the muscles, espe- 

 cially those in immediate apposition with the larger bloodvessels, and the surface- 

 markings they produce, should be carefully remembered, as they form useful 

 guides in the application of ligatures to those vessels. 



Applied Anatomy. Degeneration of muscle tissue is important clinically, and is met with 

 in two main conditions. In one, the degeneration is myopathic, or primary in the muscles 

 themselves; in the other it is neuropathic, or secondary to some lesion of the nerve system a 

 hemorrhage into the brain, for example, or injury or inflammation of some part of the spinal 



1 Hence the old name Supinator longus, now supplanted by Brachioradialis. 



- Consult in this connection the Croonian Lectures (1903) on "Muscular Movements and Their Representa- 

 tion in the Central Nervous System," by Charles K. Beevor, M.D. 



