i 9 o PRACTICAL ANATOMY. 



removing is continuous with the deep fascia covering the base of the axilla. 

 Observe the sternal and clavicular origins of the muscle. See some cutaneous 

 nerves and arteries piercing the thoracic wall, near the sternum. (Fig. 132.) The 

 arteries are the perforating branches from the internal mammary ; the nerves are 

 the anterior cutaneous branches of the intercostals. Cut the insertion of the pec- 

 toralis major. Note that the fibres that form the lower margin of the tendon 

 of the muscle are inserted high ; those that form the upper border of the muscle 

 are inserted low, into the posterior lip of the bicipital groove -of the humerus. 



Now cut the clavicular origin of the pectoralis major, and carefully pull the 

 muscle forward. On the under surface you will see the external anterior thoracic 

 nerve, a branch of the outer cord of the brachial plexus, coming through the 

 pectoralis minor muscle to supply the major pectoral muscle. Now cut the 

 sternal origin of the pectoralis major and turn the same out of the way without 

 injuring the nerve-supply. 



Digastric fascia 

 - Submaxillary fascia 

 Stylo-mandibular ligament 

 Masseteric fascia 

 Parotid fascia 



cctoral sheath 



- Axillary or suspensory fascia 



FIG. 133. To SHOW SCHEMATICALLY THE DISTRIBUTION OF THE DEEP CERVICAL FASCIA 



AND HKLOW THE CLAVICLE. 



Four very important structures, easily understood, quickly developed, and 

 seldom appreciated by the student, are now before you : 



1. The subclavius muscle and its sheath of cervical fascia. 



2. The costo-coracoid ligament, a part of subclavius sheath. 



3. The clavi-pcctoral fascia triangular and thin. 



4. The pectoralis minor muscle and its sheath. 



The third layer of deep cervical fascia passes behind the clavicle, forms a 

 sheath for the subclavius muscle, and unites along the lower margin of the sub- 

 clavius muscle to form a thick, strong band the costo-coracoid ligament. The 

 fascia then bridges the triangular space between the subclavius muscle and the 

 pectoralis muscle, under the name of clavipectoral fascia. (Fig. 132.) At this 

 point the fascia again delaminates, to form a sheath for the pectoralis minor 

 muscle. At the lower border of this muscle the fascia is continuous with the 

 deep fascia of the base of the axilla, and is known technically as the axillary 



