SHOULDER, ARM, FOREARM, AND HAND. 



191 



fascia. Let figure 133 illustrate in this connection schematically the distribution 

 of the four layers of deep cervical, both below and above. 



It will be seen from figure 133 that the first layer of deep cervical fascia is 

 specialized above the clavicle as parotid fascia, masseteric fascia, stylo-mandibular 

 ligament, submaxillary fascia, digastric fascia, and mylo-hyoid fascia ; below, the 

 first layer is attached to the clavicle. The second layer is attached above to 

 the hyoid bone, having ensheathed the depressor muscles of this bone (Fig. 24) ; 

 below, this fascia is attached to the clavicle. The fourth layer is connected to 

 the occipital bone and the muscles in front of the vertebral column. 



The third layer is of greatest importance surgically, and the most complex. 

 Passing behind the clavicle and sternum, this layer divides into a thoracic por- 

 tion, which expands to form the fibrous part of the pericardium, and also into an 

 axillary portion, which has been previously described. 



Pus formed between the first and second layers of deep cervical fascia would 

 be arrested at the clavicle. Pus formed in the carotid sheath might easily find 

 its way to either the axilla or pericardium. The student must take schematic 

 representations with a grain of allowance, remembering that fascial development, 

 like muscular development, is a variable thing, and in some cases would not 

 direct pus whither the scheme might indicate. After all, the scheme just 



POSTERIOR 



Oblique 



line for 



Capsular trapezoid Tuberosity for 

 ligament ligament conoid ligament 



Rhomboid 

 ligament and 

 Sterno- 

 hyoid Sterno-thyroid 



FACET FOR FIRST 

 COSTAL CARTILAGE 



STERNAL FACET 



ACROM1AL FACET 



Pectoralis major 

 ANTERIOR 



FIG. 134. THE LEFT CLAVICLE. (Inferior surface.) 



given is to teach that many fascial entities are definitionally only a certain seg- 

 ment of deep cervical fascia. For example : What is the subclavius sheath ? It 

 is that part of the third layer of the deep cervical fascia that invests the sub- 

 clavius muscle. What is the parotid fascia ? It is that part of the first layer of 

 deep cervical fascia which is continued above the angle of the jaw to form a 

 capsule for the parotid gland. See in the introductory chapter the rule for 

 naming specialized modifications of deep fascia in any region of the body. 



The subclavius muscle arises from the first rib, near the sternum, and is in- 

 serted into the groove on the under surface of the clavicle (Fig. 134), occupying 

 the middle two-fourths of the surface. It is surrounded by a sheath the sub- 

 clavian sheath. 



The pectoralis minor muscle arises, as a rule, from the third, fourth, and 

 fifth true ribs, and is inserted into the anterior border of the coracoid process of 

 the scapula. Its nerve is the internal anterior thoracic, a branch of the inner 

 cord of the brachial plexus. 



The clavi-pectoral space is the triangular interval you see between the upper 

 border of 'the pectoralis minor muscle and the subclavian muscle. As you will 

 see on your cadaver, this space is filled in by a delicate fascia, attached above to 

 the subclavius muscle and below to the pectoralis minor muscle. This is the 

 clavi-pectoral fascia. (Fig. 132.) 



