OF THE TRUXK. 427 



from their obliquity, rotate it, so as to turn the face to one or the other side. The 

 Longus colli flexes and slightly rotates the cervical portion of the spine. The 

 Scaleni muscles, when they take their fixed point from above, elevate the first and 

 second ribs, and are, therefore, inspiratory muscles. When they take their fixed 

 point from below, they bend the spinal column to one or the other side. If the 

 muscles of both sides act, lateral movement is prevented, but the spine is slightly 

 flexed. The Rectus lateralis, acting on one side, bends the head laterally. 



Surface Form. The muscles in the neck, with the exception of the Platysma myoides, are 

 invested by the deep cervical fascia, which softens down their form, and is of considerable 

 importance in connection with deep cervical abscesses and tumors, modifying the direction of 

 their growth and causing them to extend laterally instead of toward the surface. The Platysma 

 myoides does not influence surface form except it is in action, when it produces wrinkling of the 

 skin of the neck, which is thrown into oblique ridges parallel with the fasciculi of the muscle. 

 Sometimes this contraction takes place suddenly and repeatedly as a sort of spasmodic twitching, 

 the result of a nervous habit. The Sterno-deido-mastoid is the most important muscle of the 

 neck as regards its surface form. If the muscle is put into action by drawing the chin down- 

 ward and to the opposite shoulder, its surface form will be plainly outlined. The sternal origin 

 will stand out as a sharply-defined ridge, while the clavicular origin will present a flatter and not 

 so prominent an outline. The fleshy middle portion will appear as an oblique roll or elevation, 

 with a thick rounded anterior border gradually becoming less marked above. On the opposite 

 side i. e. on the side to which the head is turned the outline is lost, its place being occupied 

 by an oblique groove in the integument. When the muscle is at rest its anterior border is still 

 visible, forming an oblique rounded ridge, terminating below in the sharp outline of the sternal 

 head. The posterior border of the muscle does not show above the clavicular head. The 

 anterior border is defined by drawing a line from the tip of the mastoid process to the sterno- 

 clavicular joint. It is an important surface-marking in the operation of ligature of the common 

 carotid artery and some other operations. Between the sternal and clavicular heads is a slight 

 depression, most marked when the muscle is in action. This is bounded below by the prominent 

 sternal extremity of the clavicle. Between the sternal origins of the two muscles is a V-shaped 

 space, the siiprasternal notch, more pronounced below, and becoming toned down above, where 

 the Sterno-hyoid and Sterno-thyroid muscles, lying upon the trachea, become more prominent. 

 Above the hyoid bone, in the middle line, the anterior belly of the Digastric to a certain extent 

 influences surface form. It corresponds to a line drawn from the syrnphysis of the lower jaw to 

 the side of the body of the hyoid bone, and renders this part of the hyo-mental region convex. 

 In the posterior triangle of the neck, the posterior belly of the Omo-hyoid. when in action, forms 

 a conspicuous object, especially in thin necks, presenting a cord-like form running across this 

 region, almost parallel with, and a little above, the clavicle. 



MUSCLES AND FASCLE OF THE TRUNK. 



The muscles of the Trunk may be arranged in four groups : the muscles of the 

 Back, of the Thorax, of the Abdomen, and of the Perinaeum. 



THE BACK. 



The muscles of the Back are very numerous, and may be subdivided into five 

 layers. 



FIRST LAYER. FOURTH LAYER. 



Trapezius. Sacral and Lumbar Regions. 



Latissimus dorsi. -r, 



Erector spmae. 



SECOND LAYER. 



T .. Dorsal Region. 



Levator anguii scapulae. 



Rhomboideus minor. Iho-costalis. 



Rhomboideus major. Musculus accessonus ad ilio-costalem. 



Longissimus dorsi. 



THIRD LAYER. S - pinalis dorsi ' 



Serratus posticus superior. c 



Serratus posticus inferior. 



Splenius capitis. Cervicalis ascendens. 



Splenius colli. Transversalis colli. 



