1106 



SURGICAL AND TOPOGRAPHICAL ANATOMY 



Four layers must be remembered: (i) Superficial, or subcutaneous ; (ii) 

 sterno-clavicular ; (iii) tracheal; (iv) prevertebral. These should first be 

 traced horizontally, (i) Superficial, or subcutaneous. This starts from the 

 ligamentum nucha?, encases the trapezius, forms the roof of the posterior triangle, 

 where it is perforated by branches of the superficial cervical nerves and the external 

 jugular vein. Passing on, it encloses the sterno-mastoid; and, passing over the 

 anterior triangle, it meets its fellow in the middle line. Thin behind, it is thickened 

 anteriorly, where it is united to the next layer. Behind this thickened union lie 

 the anterior jugular veins, (ii) Sterno-clavicular. This is best marked below. 

 In the middle line it meets its fellow, and blends with No. i. here also. Passing 

 outwards, it encases the depressors of the hyoid bone, finall}- blending with No. i. 

 at the posterior border of the sterno-mastoid. (iii) Tracheal. This lies under the 

 depressors of the hyoid, over the trachea, also encasing the thyroid gland. Farther 

 out, it forms the carotid sheath, and, blending with No. iv. over the anterior scalene, 

 is thus brought into continuity with Nos. i. and ii. also, (iv) Prevertebral. This 

 layer passes over the longus colli and rectus capitis anticus major. 



The above layers should also be traced vertically, with especial reference to 



Fig. 679. — Diagram of the Arrangement of the Deep Cervical Fascia, the 

 Section passing through the Clavicle. (TilUiux.) 



Sterno-clavicular layer of deep 

 oervical fascia 



Subclaiian artery ^^^sft] 



Vein 



Subclavius — 



Superficial layer 



Omo-hyoid 



their relations at the level of the top of the sternum and the clavicle, (a) At the 

 level of the top of the sternum, (i) Superficial, passes over the sternum, 

 (ii) Sterno-clavicular ; this, descending in front of the depressor muscles, divides 

 just below the thyroid cartilage into two layers, which are attached to the front and 

 back of the sternum. Between these lie some fat and a small gland, (iii) Tra- 

 cheal ; this passes down over the trachea into the thorax (middle mediastinum). 

 As it descends, it encases the left innominate vein, and ends by blending with the 

 fibrous layer of the pericardium. Mr. Hilton suggested that the attachment of this 

 fascia above, and that of the central tendon of the diaphragm below, to the peri- 

 cardium served to keep this sac duly stretched, and so prevented any pressure of 

 the lungs upon the heart, (iv) Prevertebral; this, descending luOiindthe oesoph- 

 agus, dips into the posterior mediastinum. (/S) At the level of the clavicle. 

 Only two of the above layers are met Avith so far outwards as tliis — (i) Subcuta- 

 neous, which passes over the clavicle; (ii) sterno-clavicular, which, liaving 

 encased the omo-hyoid, ])asses behind the clavicle, blends with the sheath of the 

 subclavius, and gives a sheath to the subclavian vein. That to the artery is derived 

 from No. iii. at the scalenus anticus. 



