THE SUPERFICIAL CERVICAL REGION. 317 



Omo-hyoid muscle. This space extends downward behind the clavicle, and is 

 limited below by the fusion of the costo-coracoid membrane with the anterior wall 

 of the axillary sheath. (4) The pre-tracheal fascia, which extends inward in front 

 of the carotid vessels, and assists in forming the carotid sheath. It is further 

 continued behind the depressor muscles of the hyoid bone, and, after enveloping 

 the thyroid body, 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. 



Surgical Anatomy. The cervical fascia is of considerable importance from a surgical 

 point of view. As will be seen from tin- foregoing description, it may be divided into three 

 layers: (1) A superficial layer; (2) a layer passing in front of the trachea, and forming with 

 the superficial layer a sheath for the depressors of the hyoid bone; (3) a prevertebral layer 

 passing in front of the bodies of the cervical vertebrae, and forming with the second layer 

 a space in which are contained the trachea, oesophagus, etc. The superficial layer forms a com- 

 plete investment for the neck. It is attached behind to the ligamentum irachse and the spine 

 of the seventh cervical vertebra ; above it is attached to the external occipital protuberance, to 

 the superior curved line of the occiput, to the mastoid process, to the zygoma and the lower 

 jaw; below it is attached to the manubrium sterni. the clavicle, the acromion process, and the 

 spine of the scapula ; in front it blends with the fascia of. the opposite side. This layer would 

 oppose the extension of abscesses or new growths toward the surface, and pus forming beneath 

 it would have a tendency to extend laterally. If it is in the posterior triangle, it might extend 

 backward under the Trape/ius, forward under the Sterno-mastoid, or downward under the 

 clavicle for some distance, until stopped by the junction of the cervical fascia to the Costo- 

 coracoid membrane. If the pus is contained in the anterior triangle, it might find its way into 

 the anterior mediastinum, being situated in front of the layer of fascia which passes down into 

 the thorax to become continuous with the pericardium ; but owing to the lesser density and 

 thickness of the fascia in this situation it more frequently finds its way through it and points 

 above the sternum. The second layer of fascia is connected above with the hyoid bone. It 

 passes down beneath the depressors and in front of the thyroid body and trachea to become 

 continuous with the fibrous layer of the pericardium. Laterally it invests the great vessels of 

 the neck and is connected with the superficial layer beneath the Sterno-mastoid. Pus forming 

 beneath this layer would in all probability find its way into the posterior mediastinum. The 

 third layer (the prevertebral fascia) is connected above to the base of the skull. Pus forming 

 beneath this layer, in cases, for instance, of caries of the bodies of the cervical vertebrae, might 

 extend toward the posterior and lateral part of the neck and point in this situation, or might 

 perforate this layer of fascia and the pharyngeal fascia and point into the pharynx (retro- 

 pharyngeal abscess). 



In cases of cut throat the cervical fascia is of considerable importance. When the wound 

 involves only the superficial layer the injury is usually trivial, the only special danger being 

 injury to the external jugular vein, and the only special complication being diffuse cellulitis. 

 But where the second of the two layers has been opened up, important structures may have 

 been injured, which may lead to serious results. 



It may be worth while mentioning that in Burns's space is contained the sternal head of 

 origin of the Sterno-mastoid muscle, so that this space is opened in division of this tendon. 

 The anterior jugular vein is also contained in the same space. 



The Sterno-mastoid or Sterno-cleido-mastoid (Fig. 202) is a large, thick muscle, 

 which passes obliquely across the side of the neck, being enclosed 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 upward, outward, and backward. The clavicular 

 portion arises from the inner third uf the superior border and anterior surface of 

 the clavicle, being composed of fleshy and aponeurotic fibres ; it is directed almost 

 vertically upward. These two portions are separated from one another, at their 

 origin, by a triangular cellular interval, but become gradually blended, below the 

 middle of the neck, into a thick, rounded muscle, which is inserted, by a strong 

 tendon, into the outer surface of the mastoid process, from its apex to its superior 

 border, and by a thin aponeurosis into the outer half of the superior curved line 

 of the occipital bone. The Sterno-mastoid varies much in its extent of attach- 

 ment to the clavicle : in one case the clavicular may be as narrow as the sternal 

 portion ; in another, as much as three inches in breadth. When the clavicular 



