198 MUSCLES OF THE UPPER LIMB. 



ing stronger as it descends, it splits, a little below the level of the thyroid 

 body into two distinct layers. Of these the more superficial and weaker, 

 guided by the sterno-mastoid muscles, is fixed to the sternum and the 

 interclavicular ligament ; whilst the stronger layer, lying under the former, 

 and closely covering the sterno-hyoid and sterno-thyroid muscles, is 

 attached to the deeper surface of that bone. These layers materially 

 assist in closing the cavity of the chest, above the sternum : between them 

 there exists a quantity of loose connective tissue and fat, and sometimes 

 a small lymphatic gland. 



Continuous with the deeper of those two layers, a deep layer is found 

 likewise in the posterior triangle, investing the posterior belly of the omo- 

 hyoid muscle, and binding it down to the clavicle and first rib. Still deeper 

 than the processes now described is a layer which lies behind the depressor 

 muscles of the larynx, investing the thyroid body, and extending thence on 

 the trachea and large vessels at the root of the neck down to the fibrous 

 layer of the pericardium . 



Continuous with the deep processes of the cervical fascia is the common 

 sheath of the large cervical blood-vessels, an envelope of fascia enclosing the 

 carotid artery and jugular vein with the pneumogastric nerve. A thin 

 fibrous septum intervenes between the artery and vein, thus completing a 

 separate sheath for each. 



The layer of fascia descending on the prevertebral muscles, and inter- 

 vening between them and the pharynx and oesophagus, is called the pre- 

 vertebral fascia. 



MUSCLES OF THE UPPER LIMB. 



Between different parts of the head and trunk on the one hand, and the 

 shoulder and humerus on the other, certain muscles pass which attach the 

 upper limb to the body, and which, though situated mainly on the trunk, 

 and often described along with its muscles, have so intimate a connection, 

 both in their structure and uses, with the limb, that they may with greater 

 propriety be treated of along with the muscles of that part. The muscles 

 referred to are, posteriorly, the trapezius, latissimus dorsi, levator anguli 

 scapulae, and the rhomboidei ; and, anteriorly, the two pectoral muscles, the 

 subclavius, and the serratus magnus. Along with these might also be 

 mentioned the clavicular part of the sterno-cleido-mastoid muscle and the omo- 

 hyoid ; but as these last have important relations with parts situated in the 

 neck, they are more conveniently described among the muscles of that region. 



Fig. 169. SUPERFICIAL MUSCLES OP THE TRUNK, SHOULDER AND HIP, VIEWED FROM 



BEHIND. 



a, external occipital protuberance ; b, acromion of the scapula ; e, crest of the ilium ; 

 1, trapezius ; 1', oval tendon of the two muscles in the upper dorsal and lower cervical 

 region ; 1", triangular tendon of insertion ; 2, latissimus dorsi ; 2', 2', its costal origins 

 and its direct origin from the crest of the ilium ; 1, 2', c, the superficial layer of the 

 lumbar aponeurosis ; 3, sterno-mastoid ; 4, deltoid ; 5, infraspinatus ; 6, teres minor ; 

 7, teres major ; 8, rhomboideus major ; below this on the left side is seen a triangular 

 space bounded by the rhomboid, trapezius, and latissimus dorsi muscles, in which, when 

 the arm is depressed, as on the right side, a part of the seventh rib is usually felt; on the 

 left side, the arm and shoulder being elevated, the space is enlarged so as to show a part 

 of the sixth and seventh ribs ; 9, back part of the external oblique muscle of the 

 abdomen; between 9 and 2', a small part of the internal oblique ; 10, part of the gluteus 

 medius covered by the fascia lata ; 11, gluteus maximus ; 12, gracilis ; 13, small part of 

 the adductor magnus ; 14, semitendinosus ; 15, biceps ; 16, fascia lata covering the 

 vastus externus. 



