SCHULTE, SEI WHALE. 



471 



the infrahyoid muscles. From the second nerve a branch is given to the sterno-mastoid which 

 anastomoses on its deep surface with the spinal accessory, and a large branch from the third 

 behaves in a similar manner with reference to the tra- 

 pezius and masto-humeralis. These branches of the 

 second and third nerves emerge from a cleft in the 

 scalene, in its upper third and on its ventrolateral as- 

 pect, not in line with the more ventral cleft in the caudal 

 third of the muscle, which gives passage to the brachial 

 plexus. The phrenic nerve emerges from the ventro- 

 mesal aspect of the scalene, opposite the middle of the 

 cleft for the plexus. It is derived mainly from the 

 fourth nerve but on the right was joined by a small 

 branch of the fifth. These first four cervical nerves join 

 in the supply of the scalene and hypaxial muscles of the 

 neck. The suboccipital nerve gives branches to the 

 rectus capitis lateralis and to the obliquus. All com- 

 municate with the large superior cervical ganglion of 

 the sympathetic. 



Brachial plexus. The ventral divisions of the 

 nerves entering into this plexus increase in size caudad 

 to the eighth cervical, which is at least ten times the 

 size of the fifth; the first thoracic is of large size but 

 distinctly less than that of the eighth cervical. In the 

 scalene cleft the usual primary trunks are formed, the 

 upper by the union of the fifth and sixth, the lower by 

 that of the eighth cervical and the first thoracic, while 

 the seventh cervical remains single forming a middle 

 trunk. Before emergence the upper and middle trunks 

 unite to form a short upper cord, which promptly resolves itself into branches of distribution 

 and anastomosis. Of the latter one joins the lateral cutaneous branch of the lower trunk, its 

 fibres being largely but not entirely continued into the internal anterior thoracic nerves to the 

 pectoralis. The other anastomotic branch joins with a similar branch of the lower trunk in a 

 loop, from the apex of which is given off the combined circumflex and musculo-spiral trunk. It 

 is therefore representative of the posterior cord of more usual plexus types, the chief peculiarity 

 being incident to the complete union of the upper and middle primitive trunks prior to the 

 origin of the so-called posterior branches, so that these are represented by a common branch, 

 which in addition to the usual components carries fibres destined for the musculo-cutaneous 

 nerve. There is further no separate median nerve. 



The suprascapular nerve is given off from the short cord resulting from the union of the 

 upper and middle trunks. It enters the interval between subscapularis and supraspinatus, 

 the latter of which it supplies, and passing between the supraspinatus and the border of the 

 scapula crosses the bone dorsally to reach the infraspinatus. 



The subscapular nerves are three in number. They are derived from the lateral branch 

 of communication of the upper cord; the third is the largest and ends in the teres major. The 



Fig. 6. Schema of brachial plexus. 1, Supra- 

 scapular nerve. 2, Subscapular nerves. 3, Musculo- 

 cutanens nerve. 4, Musculo-spiral nerve. 5, Circum- 

 flex nerve. 6, Ulnar nerve. 7, Internal cutaneous 

 nerve. 8, Nerve of the latissimus dorsi. 9, Nerve of 

 the panniculus carnosus. 10, Anterior thoracic nerves. 



