40 ANATOMY IX A NUTSHELL. 



by its base to the conoid tubercle of the clavicle and a line running internally 

 for half an inch: below by its apex to the rough impression at the base of the 

 coracoid process. 



Blood Supply.- The nutrient artery of the clavicle is from the supra- 

 scapular. The acromial end receives a branch from the acromial thoracic 

 artery and twigs from the arteries in the muscles attached to it. 



LESSON VIII. 



Muscles. 



'The muscles of the clavicle are six. viz., Sterno-cleido-mastoid. Sterno- 

 hyoid, Subclavius, Pectoralis major. Deltoid, Trapezius, and occasionally the 

 Sterno-thyroid. 



Sterno-cleido-mastoid; Description. — (Plate (XIV.) This muscle passes 

 obliquely across the side of die neck and is enclosed between the two layers of 

 the deep cervical fascia. It is broad and thin at each extremity, hut is thicker 

 mm. I narrower at the central portion. The portion which is attached to the 

 sternum is directed upward, backward and outward. This attachment is ten- 

 dinous in front and fleshy behind. The portion which is attached to the clav- 

 icle is directed almosl vertically upward and is composed of fleshy and aponeu- 

 rotic fibers. These two portions are separated at their origin, but become 

 gradually Mended below the middle of the neck into a thick, round muscle. 

 The attachment of this muscle to the clavicle may he as small as the sternal 

 attachment or it may extend to the attachment of the trapezius muscle at the 

 outer portion of the clavicle. This muscle divides the quadrilateral space at 

 the side of the neck into two triangles, an anterior and posterior. 



Origin. By two heads; first from the anterior surface of the upper part 

 of the manubrium of the sternum; the second from the inner one-third of the 

 superior border ami anterior surface of the clavicle. (Plate XI.) 



Insertion. Mastoid process of temporial bone and the outer two-thirds 

 or one half of the superior curved line of the occipital bone. 



Action. To depress and rotate head and elevate the thorax. 



Nerve Supply. Spinal accessory (eleventh cranial) and deep branches 

 of the cervical plexus (second and (third'.') nerves.) 



Blood Supply. The superior sterno-mastoid artery from the occipital 

 artery, the middle sterno-mastoid artery from the superior thyroid artery, the 

 inferior sterno-mastoid artery from the suprascapular artery, also branches 

 from the posterior auricular artery. 



Sterno-hyoid. Description. The sterno-hyoid covers the thyroid gland 

 and upper pari of the trachea, and is a thin narrow muscle, its lower portion 

 being immediately beneath the Sterno-mastoid. This muscle comes in contact 

 with its fellow in the middle of their course, and from there on lie side by side, 

 but they are separated below from each other by a considerable interval. 



Origin, i 1 i Posterior surface of the manubrium of the sternum. (2) ster- 

 nal end of the clavicle and posterior sterno-clavicular ligament. 



