336 



THE MUSCLES AND FASCIA 



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 suprasternal 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 symphysis 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 FASCLffi OF THE TRUNK. 



The muscles of the Trunk may be arranged in four groups, corresponding 

 with the region in which they are situated. 



I. The Back. 

 II. The Thorax. 



III. The Abdomen. 



IV. The Perinaeum. 



I. MUSCLES OF THE BACK. 



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

 layers : 



FIRST LAYER. Longissimus dorsi. 



Trapezius. Spinalis dorsi. 



Latissimus dorsi. 



Cervical Region. 



SECOND LAYER. Cervicalis ascendens. 



Transversalis cervicis. 



Levator anguli scapulae. Trachelo-mastoid. 



Rhomboideus minor. Complexus. 



Rhomboideus major. Biventer cervicis. 



Spinalis colli. 

 THIRD LAYER. 



Serratus posticus superior. 

 Serratus posticus inferior. 

 Splenius capitis. 

 Splenius colli. 



FOURTH LAYER. 



Sacral and Lumbar Regions. 

 Erector spinee. 



Dorsal Region. 



Ilio-costalis. 



Musculus accessorius ad ilio-costalem. 



Trapezius. 



First Layer. 



FIFTH LAYER. 



Semispinalis dorsi. 

 Semispinalis colli. 

 Multifidus spinse. 

 Rotatores spinae. 

 Supraspinales. 

 Interspinales. 

 Extensor coccygis. 

 Intertransversales. 

 Rectus capitis posticus major. 

 Rectus capitis posticus minor. 

 Obliquus capitis inferior. 

 Obliquus capitis superior. 



Latissimus dorsi. 



Dissection (Fig. 212). Place the body in a prone position, with the arms extended 

 over the sides ot the table, and the chest and abdemen supported by several blocks, so as 

 to render the muscles tense. Then make an incision along the middle line of the back from the 

 occipital protuberance to the coccyx. Make a transverse incision from the upper end of this to 



