THE CERVICAL MUSCLES. 543 



the greater cornu and body of the hyoid bone, to which it is firmly attached, and 

 where it becomes continuous above with the deep fascia of the submental region. 

 This fascia covers in the anterior belly of the digastric, the mylo-hyoid, and the 

 submaxillary gland, and is attached above to the lower border of the mandible, 

 where it becomes continuous with the parotideo-masseteric fascia. 



Below the cervical fascia ends over the anterior surface of the clavicle, and, 

 more medially, in the interval between the lower portions of the two sterno-cleido- 

 mastoid muscles, it splits into two lamellae, enclosing what is termed the spathmi 

 siiprasternale or space of Burns. Both the lamellae pass down to be attached to the 

 upper part of the manubrium sterni, so that the suprasternal space is completely 

 closed. It contains some fatty tissue, usually some lymphatic nodes, and the lower 

 portions of the anterior jugular veins ; a diverticulum from it is prolonged laterally 

 behind the insertion of the sterno-cleido-mastoid along each vein as it passes towards 

 its point of union with the subclavian vein. 



From the under surface of this superficial layer a deeper or middle layer is 

 given off at the sides of the neck, and, passing forward, assists in the formation of 

 the sheath for the carotid artery and internal jugular vein, and then divides to 

 enclose the omo-hyoideus and the other depressors of the hyoid bone, a special 

 thickening of it extending downward from the intermediate tendon of the omo-hyoid 

 to the clavicle. Above, the middle layer is attached to the greater cornu and body 

 of the hyoid bone along with the superficial layer, but below it is continued down 

 into the thorax in front of the oesophagus and trachea and becomes lost upon the 

 upper part of the pericardium. 



A third or deep layer of the cervical fascia, also termed the prevertebral fascia, 

 is given off from the under surface of the superficial layer about on the line of the 

 transverse processes of the vertebrae. It passes almost directly inward over the 

 scalene and hyposkeletal muscles of the neck, enclosing the cervical portion of the 

 sympathetic trunk and contributing to the formation of the carotid sheath. It 

 unites with the corresponding layer of the opposite side over the bodies of the 

 vertebrae. This fascia is continued downward into the thorax in front of the verte- 

 bral column and above it extends to the base of the skull. Towards the median 

 line in its upper part it is separated from the pharyngeal portion of the fascia 

 bucco-pharyngea by some loose areolar tissue which occupies the so-called retro- 

 pharyngeal space. This is continued downward in the loose tissue surrounding the 

 oesophagus, but is bounded laterally by the union of the pharyngeal and prevertebral 

 fasciae. 



The carotid sheath is formed by the union of portions from the middle and deep 

 layers of the cervical fascia. It forms an investment for the common carotid artery, 

 the internal jugular vein, and the vagus nerve. 



{a) THE RECTUS MUSCLES. 



1. Sterno-hyoideus. 3. Sterno-thyroideus. 



2. Omo-hyoideus. 4- Thyro-hyoideus. 



5. Genio-hyoideus. 



I. Sterno-Hyoideus (Fig. 541). 



Attachments. — The sterno-hyoid is a flat band-like muscle situated in the 

 front of the neck close to the median line. It arises from the posterior surface of 

 the sternal end of the clavicle and from the manubrium sterni and passes upward to 

 be inserted into the lower border of the body of the hyoid bone. A mucous bursa, 

 more constant in the male than in the female, usually occurs beneath the upper 

 part of the muscle, resting upon the hyo-thyroid membrane near the median line 

 and immediately below the hyoid bone. 



Nerve-Supply. — From the first, second, and third cervical nerves, through 

 the ansa hypoglossi. 



Action. — To draw the hyoid bone downward. 



