The; Anterior Limb. 135 



VIII. THE ANTERIOR LIMB. 



For this dissection the skin must first be reflected from the lateral 

 surface of the limb and the side of the neck to the dorsal median line. 

 Covering the side and ventral surface of the neck is a broad thin sheet of 

 muscle, the platysma, replacing the cutaneus maximus of the trunk. It 

 forms a continuous layer over the dorsal surface of the neck, at which 

 place it is also continuous with the cutaneus maximus. Passing 

 forward from the manubrium sterni is a narrow band of fibres, in- 

 separable from the platysma but lying beneath it, the depressor conchae 

 (parotideoauricularis) posterior, which is inserted into the external base 

 of the ear. The entire sheet of muscle should be raised from the surface, 

 separated posteriorly from its attachment, and turned forward on the 

 head. 



The dissection is mainly muscular, but the arteries and nerves should 

 be kept intact for later examination. 



For the general muscular relations of anterior and posterior limbs see p. 33. 



*1. Muscles arising from the axial skeleton and inserted on the 

 scapula and clavicle. 



(a) The cleidomastoideus. Origin : Mastoid portion of the skull. 

 Insertion : Middle portion of the clavicle. 



The muscle lying on its medial side and arising from the manubrium 

 sterni is the sternomastoideus, one of the muscles of the head. 



(b) The basioclavicularis (basiohumeralis). Origin: Basiocci- 

 pital bone. Insertion: Lateral third of the clavicle and the 

 cleidohumeral ligament. 



(c) The levator scapulae major. Origin: Sphenooccipital syn- 

 chondrosis. Insertion: Metacromion. 



The superficial cervical artery (p. 173) passes obliquely forward and 

 outward under cover of the'se muscles, ramifying beneath the 

 superior portion of the trapezius in the fat-mass of the side of the 

 neck. Its ascending cervical branch passes forward on the lateral 

 surface of the external jugular vein. 



(d) The trapezius. Origin in two portions : 



Superior (cervical) portion: External occipital protuberance and 

 the ligamentum nuchae. Insertion: Metacromion and 

 supraspinous fascia. 



Inferior (thoracic) portion. Origin: Spinous processes of the 

 thoracic vertebrae and the lumbodorsal fascia. Insertion : 

 Dorsal two- thirds of the scapular spine. The muscle forms 

 a broad triangular sheet on the lateral surface of the shoulder. 

 The levator scapulae major, basioclavicularis, and trapezius should 

 be divided. On the ventral surface of the origin of the superior 

 portion of the trapezius and levator scapulae- major may be found 

 the ventral rami of the third and fourth cervical spinal nerves. The 

 great auricular nerve (n. auricularis magnus) passes from the third to 

 the ear. 



*The structures of Group 2 may be dissected first if preferred, the serratus 

 anterior muscle being exposed from the lateral surface and divided together with 

 the latissimus dorsi. 



