AT. PHRENICUS. 383 



brachial plexus to the pectoral region. It is divided into two parts, 

 or rather there are two nerves an ectal or cephalic division, accom- 

 panying the anterior thoracic artery between the muscles ( 939), 

 and an ental or caudal division, accompanying the long thoracic 

 artery ( 940), and distributed to the pectoral and also somewhat 

 to the latissimus muscle. The two are connected near their origin 

 by an anastomosing branch, as shown in Fig. 105 and 106. 



Dissection. If the section was properly made through the pec- 

 toral muscles, the ectal or cephalic division will be turned mesad and 

 the ental division laterad. Both are easily found, and their relations 

 and distribution can be determined by using the tracer and fine 

 forceps. 



1019. N. phrenicus s. diaphragmaticus (Fig. 103, 105, 107 ; 

 Quain, A, I, 578 ; Gray, A, 669). This nerve is formed by two 

 branches, one from the 5th and one from the 6th cervical nerve. It 

 also occasionally receives a branch from the 4th cervical, as in man. 

 The latter condition is shown in Fig. 105, while the more frequent one 

 is shown in Fig. 107. These branches unite near the 1st rib, and the 

 phrenic then passes into the thorax on the mesal side of the A. ster- 

 nalis (Fig. 107, 109). The right nerve rests on the lateral aspect of 

 the prse- and postcavse on its way to the diaphragm, to which it is 

 distributed. The course of the left is well shown in Fig. 103 and 

 107, N. phrn. 



Dissection. The branches forming the phrenic nerve are quite 

 small, hence it is best to trace the nerve centrad from the point 

 where it enters the thorax ; the branches may then be isolated one 

 by one. When this is done, the costicartilages and the thoracic 

 walls may be cut and the two edges divaricated. The nerve will 

 appear very clearly as a white cord passing along the lateral aspect 

 of the prse- and postcavse to the diaphragm. 



1020. N. suprascapularis (Fig. 104, 105, 106 ; Quain, A, I, 583 ; 

 Gray, A, 672). The suprascapular nerve arises from the 6th cervi- 

 cal. It passes directly laterad for a short distance and then divides 

 into two branches, one going to the ental surface of the M. clavo- 

 deltoideus, the other to the ectal surface of the scapula. These two 

 branches accompany the branches of the suprascapular artery 

 ( 937). 



Dissection. This nerve is easily traced. It follows closely the 

 corresponding branches of the suprascapular artery, and may be 

 traced as directed for that vessel ( 937). 



