The; Anterior Limb. 137 



of the second portion and those of the pectoscapularis, pass 

 to the dorsal side of the clavicle and over the shoulder to be 

 inserted on the scapular spine. 



(e) The pectoralis quartus. Origin: The sternum, from the 

 attachment of the fourth to seventh costal cartilages, in- 

 sertion : Anterior surface of the head of the humerus, passing 

 thence to its medial side. The muscle overlaps the more 

 posterior fibres of the first portion of (d). 



(f) The pectoscapularis. Origin: The sternum at the point of 

 attachment of the first costal cartilage. Insertion as indi- 

 cated above. A slender muscle lying behind and lateral to 

 the second portion of (d). In order to make out its extent 

 the first portion of (d) should be divided. 



Bloodvessels and Nerves of the Axillary Fossa. 



By dividing the remaining pectorals and the clavicle, the blood- 

 vessels and nerves of the axillary fossa will be exposed. 



*The axillary artery (a. axillaris), the continuation of the subclavian, 

 crosses from the first rib to the medial surface of the humerus, where it 

 is replaced by the brachial artery. Its branches include : 



(a) The thoracoacromial artery (a. thoracoacromialis) ; it arises 

 from the anterior wall and passes laterad to the shoulder, reach- 

 ing the latter at a point directly above and in front of the head 

 of the humerus. A superficial branch of this artery passes 

 between the pectoralis primus and the deltoideus, giving 

 twigs on either side. 



(b) The lateral (long) thoracic artery (a. thoracalis lateralis) is a 

 larger branch given off from the posterior wall. Its branches 

 include short anterior vessels to the pectoral muscles and 

 long (external mammary) branches, especially developed in 

 the female, to the side of the thorax. 



(c) The subscapular artery (a. subscapularis) is a large branch 

 which passes around the axillary border of the scapula, per- 

 forating the teres major muscle, and is distributed to the 

 muscles of this region, including the cutaneus maximus. A 

 branch of this vessel, the thoracodorsal artery (a. thoraco- 

 dorsalis), passes backward to the latissimus dorsi. 



The superficial cervical artery (p. 173) crosses the ventral surface 

 of the brachial plexus, passing obliquely laterad to the side of the 

 neck. 



(d) The deep artery of the arm (a. profunda brachii) is given off 

 at about the point of origin of the subscapular. It passes 

 to the posterior surface of the humerus giving branches to 

 the shoulder, and is continued distad on the lateral surface 

 of the anconaeus medialis and afterwards of the lateral head 

 of the brachialis as the radial collateral artery. This artery 

 accompanies the branches of the radial nerve. 



