754- 



SPINAL NERVES. 



its origin principally from the descending di- 

 vision of the second cervical, and having re- 

 ceived a filament from the first cervical, comes 

 down the neck external and posterior to the 

 internal jugular vein. At the middle or lower 

 third of the neck, it describes a curve ; the 

 concavity of which looks upwards, and com- 

 municates with the descending branch of the 

 lingual (descendens noni), by winding in front 

 of the internal jugular vein. This nerve is 

 subject to considerable variation, bifurcating, 

 occasionally, before communicating with the 

 descendens noni, and giving off now and then 

 one or two delicate filaments to the same 

 muscles, usually supplied by the latter nerve : 

 viz. the sterno-hyoid, sterno-thyroid, and 

 omo-hyoid. The external communicating 

 branches are represented by a rather larger 

 anastomotic branch, which communicates at an 

 acute angle with the spinal accessory ; and by 

 the muscular branches. These accompany the 

 spinal accessory, communicate more or less 

 with it, and are distributed to the trapezius, le- 

 vator anguli scapulae, the rhomboideus minor, 

 and upper part of the rhomboideus major. 



The phrenic nerve (diaphragmatic, internal 

 respiratory) appears at the lower and anterior 

 part of the fourth cervical nerve of which it 

 appears the continuation. It receives, how- 

 ever, some accessory filaments from the third 

 and fifth cervical, which exist either as single 

 or plexiform twigs, or are occasionally absent. 

 The secondary sources of origin are, in fact, 

 subject to considerable variation. It is di- 

 rected along the anterior edge of the scalenus 

 anticus, inclining slightly inwards between the 

 subclavian artery and vein, before entering 

 the superior opening of the thorax. It passes 

 behind and outside the carotid artery and 

 jugular vein, and communicates with the 

 fifth, sixth, and, occasionally, with the seventh 

 cervical and pneumogastric nerves, and in- 

 variably with the sympathetic. The exact 

 points of communication of these different 

 nerves is by no means determinate ; some- 

 times taking place in the neck ; at others, in 

 the upper part of the chest. It crosses the 

 direction of the internal mammary artery, and 

 reaching the anterior mediastinum, glides 

 down in front of the root of the lung between 

 the pericardium and inner aspect of the former, 

 and terminates in the diaphragm. In its 

 course within the chest, it gives several fila- 

 ments to the remains of the thymus gland ; 

 some very minute twigs of communication 

 with the superior cardiac plexus ; and re- 

 ceives, occasionally, a very delicate filament 

 of communication, coming down obliquely, 

 from the descendens noni : on reaching the 

 diaphragm, the nerve divides into a series of 

 superior and inferior filaments ; the former, 

 long and diverging from each other, enter the 

 upper surface of the muscle, having first 

 passed for some distance between the muscle 

 jmd the pleura covering it; the latter per- 

 forate the muscle, diverge, and run for some 

 distance between the muscle and peritoneum, 

 and enter its under surface. 



The right phrenic is shorter and more ver- 



tical in direction, and more anterior in its 

 position than the left, being directed in the 

 upper part of the chest, along the vena cava 

 superior. Several of its internal terminal 

 filaments pass behind the vena cava inferior, 

 communicate with the left, and end in the 

 coeliac plexus ; a few, however, communi- 

 cate, also, with some twigs of the pneumo- 

 gastric. 



The left phrenic turns over the apex of 

 the heart; and, besides its general distribu- 

 tion, gives filaments to the crura of the dia- 

 phragm, anastomosing filaments to the solar 

 and cceliac plexus, and some communicating 

 branches to the opposite nerve, 



The anterior branches of the four inferior 

 cervical and first dorsal nerves are very large, 

 and form, therefore, a remarkable contrast to 

 the four upper cervical, situated above them. 

 They pass through the intervertebral foramina, 

 between the two scaleni ; the eighth cervical 

 passing between the foramen common to the 

 last cervical and first dorsal vertebra. Having 

 given off several filaments to communicate 

 with similar filaments from the inferior and 

 middle cervical ganglion, and some small 

 twigs to the scaleni, the different branches 

 unite together, so as to constitute the bra- 

 chial plexus; the first, communicating above 

 with the fourth cervical, and sending a twig 

 to the phrenic. The union of the different 

 branches takes place in the following manner : 

 the anterior branches of the fifth and sixth 

 descend obliquely outwards, and, after a 

 course of about one or two inches, unite at 

 an acute angle. Those of the eighth cervical 

 and first dorsal, which are not so oblique in 

 their direction, similarly unite; but a little 

 more internally : this union taking place, oc- 

 casionally, between the scaleni, either pair of 

 branches almost immediately bifurcating after 

 their union. The trunk of the seventh passes 

 distinct between the two upper and lower 

 branches, as far as the lower border of the 

 clavicle in the upper part of the axilla, and 

 there bifurcates ; the upper part of the bifur- 

 cation being connected with the lower part of 

 the bifurcation of the first united cord, and 

 the lower with the upper of the last united 

 cord. Secondary bifurcations and anasto- 

 moses take place at more or less acute angles, 

 and thus the brachial plexus is constituted. 



The brachial plexus (axillary) is situated at 

 the inferior and lateral part of the neck, in the 

 posterior inferior cervical triangle, where it is 

 covered in by a considerable quantity of fat, 

 cellular membrane,and lymphatic glands, which 

 separate it from the external jugular vein. 

 The scalenus anticus bounds it in front and 

 internally ; the scalenus posticus in the oppo- 

 site direction ; and in its course from between 

 these muscles to the clavicle, it is crossed by 

 the omo-hyoid muscle, transversalis coli, and 

 humeral vessels, and more superficially, by 

 the supra-clavicular and acromial branches of 

 the cervical plexus. Having passed from 

 beneath the clavicle, it becomes placed be- 

 tween the coracoid process of the scapula and 

 the first digitation of the serratus magnus, 



