270 A MANUAL OF ANATOMY. 



it runs upward in the groove at the outer margin of the 

 biceps muscle, then enters the interval between the deltoid 

 and pectoralis major muscles, to finally pierce the costo- 

 coracoid membrane in front of the clavicle and empty into 

 the axillary vein. In the course between the last muscles 

 it is accompanied by the descending (humeral) branch of 

 the acromiothoracic artery. 



DISSECTION. 



Section the pectoralis major at its middle and outer thirds, and cut it away 

 from the clavicle. Raise the parts and reflect them. Notice the formation 

 and method of insertion of the tendon, and the nerve and arterial supply to 

 the inner part of the muscle. Carefully expose the deep fascia (costocouacoid 

 membrane). The nerves and arteries exposed can now be completed. 



The Costocoracoid Membrane. Fig. 61. 



This starts from the under surface of the clavicle in two 

 layers, one in front, the other behind the subclavius muscle. 

 These two layers become united along the front of the 

 muscle and form a single plane of fascia that spreads 

 downward to the pectoralis minor muscle, inward to the 

 first rib and cartilage, and the aponeurosis of the first inter- 

 costal space, and outward to the coracoid process. The 

 portion of the membrane between the coracoid process and 

 the first costal cartilage is much thicker and stronger than 

 any other part of the membrane, and is known as the costo- 

 coracoid ligament. 



The costocoracoid membrane is perforated by the 

 cephalic and acromiothoracic veins, the acromiothoracic 

 artery, the external anterior thoracic nerve, and the axillary 

 lymphatic trunk. 



The outward continuation of this membrane is in the 

 shape of two layers of thin fascia which enclose the pector- 

 alis minor muscle, unite at the lower margin of the same, 



