332 MUSCLES AND FASCIAE. 



closely below, but more loosely above. By its internal surface, with the Pec- 

 toralis Major, Deltoid, and Trapezius, and with the clavicle. In the neck, with 

 the external and anterior jugular veins, the deep cervical fascia, the superficial 

 cervical plexus, the Sterno-mastoid, Sterno-hyoid, Omo-hyoid, and Digastric 

 muscles. In front of the Sterno-mastoid, it covers the sheath of the carotid 

 vessels; and behind it, the Scaleni muscles and the nerves of the brachial 

 plexus. On the face, it is in relation with the parotid gland, the facial artery 

 and vein, and the Masseter and Buccinator muscles. 



The deep cervical fascia is exposed on the removal of the Platysma Myoides. 

 It is a strong fibrous layer, which invests the muscles of the neck, and incloses 

 the vessels and nerves. It commences, as an extremely thin layer, at the back 

 part of the neck, where it is attached to the spinous processes of the cervical 

 vertebra, and to the ligamentum nuchae ; and, passing forwards to the posterior 

 border of the Sterno-mastoid muscle, divides into two layers, one of which 

 passes in front, and the other behind that muscle. These join again at the 

 anterior border of the Sterno-mastoid ; and, being continued forwards to the 

 front of the neck, blend with the fascia of the opposite side. The superficial 

 layer of the deep cervical fascia (that which passes in front of the Sterno- 

 mastoid), if traced upwards, is found to pass across the parotid gland and 

 Masseter muscle, forming the parotid and masseteric fascia, and is attached to 

 the lower border of the zygoma, and more anteriorly to the lower border of 

 the body of the jaw ; if the same layer is traced downwards, it is seen to pass 

 to the upper border of the clavicle and sternum, being pierced just above the 

 former bone by the external jugular vein. In the middle line of the neck, the 

 fascia is thin above, and connected to the hyoid bone ; but it becomes thicker 

 below, and divides, just below the thyroid gland, into two layers, the more 

 superficial of which is attached to the upper border of the sternum and inter- 

 clavicular ligament ; the deeper and stronger layer is connected to the posterior 

 border of that bone, covering in the Sterno-hyoid and Sterno-thyroid muscles. 

 Between these two layers is a little areolar tissue and fat, and occasionally a 

 small lymphatic gland. The deep layer of the cervical fascia (that which lies 

 behind the posterior surface of the Sterno-mastoid) sends numerous prolonga- 

 tions, which invest the muscles and vessels of the neck ; if traced upwards, a 

 process of the fascia, of extreme density, is found passing behind and to the 

 inner side of the parotid gland, to be attached to the base of the styloid pro- 

 cess and angle of the lower jaw, termed the stylo-maxillary ligament ; if traced 

 downwards and outwards, the fascia will be found to inclose the posterior belly 

 of the Omo-hyoid muscle, binding it down by a distinct process, which descends 

 to be inserted into the clavicle and cartilage of the first rib. The deep layer 

 of the cervical fascia also assists in forming the sheath which incloses the 

 common carotid artery, internal jugular vein, and pneumogastric nerve. There 

 are fibrous septa intervening between each of these parts, which, however, are 

 included together in one common investment. More internally, a thin layer is 

 continued across the trachea and thyroid gland, beneath the Sterno-thyroid 

 muscles ; and at the root of the neck this may be traced, over the large vessels, 

 to be continuous with the fibrous layer of the pericardium. 



The Stemo-ckido-mastoid (Fig. 220) is a large thick muscle which passes 

 obliquely across the side of the neck, being inclosed between the two layers 

 of the deep cervical fascia. It is thick and narrow at its central part, but is 

 broader and thinner at each extremity. It arises, by two heads, from the 

 sternum and clavicle. The sternal portion is a rounded fasciculus, tendinous in 

 front, fleshy behind, which arises from the upper and anterior part of the first 

 piece of the sternum, and is directed upwards and backwards. The ^du vicula r 

 portion arises from the inner third of the superior border of the clavicle, being 

 composed of fleshy and aponeurotic fibres ; it is directed almost vertically up- 

 wards. These two portions are separated from one another, at their origin, by 

 a triangular cellular interval ; but become gradually blended, below the middle 



