390 MYOLOGY 



prevertebral fascia is fixed above to the base of the skull, and below is continued 

 into the thorax in front of the Longus colli muscles. Parallel to the carotid sheath 

 and along its medial aspect the prevertebral fascia gives off a thin lamina, the 

 buccopharyngeal fascia, which closely invests the Constrictor muscles of the pharynx, 

 and is continued forward from the Constrictor pharyngis superior on to the Buc- 

 cinator. It is attached to the prevertebral layer by loose connective tissue only, 

 and thus an easily distended space, the retropharyngeal space, is found between 

 them. This space is limited above by the base of the skull, while below it extends 

 behind the esophagus into the posterior mediastinaf cavity of the thorax. The pre- 

 vertebral fascia is prolonged downward and lateralward behind the carotid vessels 

 and in front of the Scaleni, and forms a sheath for the brachial nerves and sub- 

 clavian vessels in the posterior triangle of the neck; it is continued under the clavicle 

 as the axillary sheath and is attached to the deep surface of the coracoclavicular 

 fascia. Immediately above and behind the clavicle an areolar space exists between 

 the investing layer and the sheath of the subclavian vessels, and in this space are 

 found the lower part of the external jugular vein, the descending clavicular nerves, 

 the transverse scapular and transverse cervical vessels, and the inferior belly of the 

 Omohyoideus muscle. This space is limited below by the fusion of the coraco- 

 clavicular fascia with the anterior wall of the axillary sheath. (4) The pretrachial 

 fascia extends medially in front of the carotid vessels, and assists in forming the 

 carotid sheath. It is continued behind the depressor muscles of the hyoid bone, 

 and, after enveloping the thyroid gland, is prolonged in front of the trachea to 

 meet the corresponding layer of the opposite side. Above, it is fixed to the hyoid 

 bone, while below it is carried downward in front of the trachea and large vessels 

 at the root of the neck, and ultimately blends with the fibrous pericardium. This 

 layer is fused on either side with the prevertebral fascia, and with it completes the 

 compartment containing the larynx and trachea, the thyroid gland, and the pharynx 

 and esophagus. 1 



The Sternocleidomastoideus (Sternomastoid muscle) (Fig. 385) passes obliquely 

 across the side of the neck. It is thick and narrow at its central part, but broader 

 and thinner at either end. It arises from the sternum and clavicle by two heads. 

 The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, 

 which arises from the upper part of the anterior surface of the manubrium sterni, 

 and is directed upward, lateralward, and backward. The lateral or clavicular head, 

 composed of fleshy and aponeurotic fibers, arises from the superior border and 

 anterior surface of the medial third of the clavicle; it is directed almost vertically 

 upward. The two heads are separated from one another at their origins by a 

 triangular interval, but gradually blend, below the middle of the neck, into a thick, 

 rounded muscle which is inserted, by a strong tendon, into the lateral surface of 

 the mastoid process, from its apex to its superior border, and by a thin aponeurosis 

 into the lateral half of the superior nuchal line of the occipital bone. 



Variations. The Sternocleidomastoideus varies much in the extent of its origin from the clavicle: 

 in some cases the clavicular head may be as narrow as the sternal ; in others it may be as much 

 as 7.5 cm. in breadth. When the clavicular origin is broad, it is occasionally subdivided into 

 several slips, separated by narrow intervals. More rarely, the adjoining margins of the Sterno- 

 cleidomastoideus and Trapezius have been found in contact. The Supradavicularis muscle arises 

 from the manubrium behind the Sternocleidomastoideus and passes behind the Sternocleido- 

 mastoideus to the upper surface of the clavicle. 



Triangles of the Neck. This muscle divides the quadrilateral area of the side of the neck 

 into two triangles, an anterior and a posterior. The boundaries of the anterior triangle are, in 

 front, the median line of the neck; above, the lower border of the body of the mandible, and an 

 imaginary line drawn from the angle of the mandible to the Sternocleidomastoideus; behind, 

 the anterior border of the Sternocleidomastoideus. The apex of the triangle is at the upper 



1 F. G. Parsons (Journal of Anatomy and Physiology, vol. xliv) regards the carotid sheath and the fascial planee 

 in the neck as structures which are artificially produced by dissection. 



