BY W. J. S. McKAY. 349 



The posterior division of the third nerve, after giving origin to 

 the phrenic, sends a large branch to the levator scnpulje portion 

 of the serratus magaus (20) ; then a branch to the fourth cervical 

 nerve, and then numerous cutaneous and communicating twigs to 

 the side of the neck (6, 10). 



N. cervicalis iv. This divides into two divisions. The anterior 

 runs outwards to the lateral aspect of the neck, where it is joined 

 by branches from the third nerve, and after this it sends branches 

 posteriorly over the clavicular region. The posterior division runs 

 posteriorly, and after communicating with the phrenic it joins the 

 fifth cervical nerve. 



Plexus brachialis. The brachial |)lexus is formed by v., vi., vii., 

 and viii. cervical, and i dorsal nerves, together with branches 

 from the iv. cervical and ii. dorsal nerves After the bianch 

 from the fourth nerve has joined the fifth, there spring from the 

 junction the following branches : — {a) A twig to the phrenic (21a). 

 (6) The nerve to supply the costo-coracoid (21) and sterno-epicora- 

 coid muscles (21i). This nerve runs posteriorly and inwards, 

 giving off two twigs to the phrenic in its course ; and having 

 entered the costo-coracoid it supplies this muscle and ends in the 

 sterno-epicoracoid. (c) The N.supracoracoideus (22) is a large trunk 

 which takes an antero- ventral course, and emerging between the 

 epicoraco-hnmeral and the supraspinatus, and having sent a branch 

 to supply the latter (2.5) muscle and the infraspinatus (26), it then 

 supplies the epicoraco-hnmeral (22a) ; it gives off a minute twig 

 which runs towards the median line and emerges between the 

 pectoralis major and the clavicular part of the deltoid. The 

 remainder of the nerve stem pierces the clavicular deltoid (and 

 may possibly give this muscle a minute branch), and then becomes 

 cutaneous, "ramus cutaneus N. supracoracoideus " (vide further 

 remarks on this nerve, post), (d) Accord (-51) which joins cords 

 from the vi. and vii. cervical nerves, (e) A cord (.52) which joins 

 one of the divisions into whic'i the vi. nerve divides. 



A"^. cervicalis vi. Before this nerve divides it sends a small 

 branch to join a twig from the fifth nerve to supply the serratus. 

 2-t 



