756 THE NERVES. 



magnus). It soon divides into several filaments, which are wholly expended 

 in the substance of that muscle, the serratus magnus, and the rhombdideus. 

 The filament supplying the latter is slender and very long, and, to reach its 

 destination, passes through the angularis. 



3. Serratus Magnus, or Superior Thoracic Branch. (Fig. 347, 8.) 



This very remarkable branch proceeds by two principal portions from 

 the fasciculus common to all the divisions of the brachial plexus: one 

 emanating from the sixth cervical pair ; the other from the seventh, and 

 always traversing the last fasciculus of the scalenus before joining the first. 

 The single branch resulting from the union of these two roots is thin and 

 very wide. It passes back to the surface of the serratus magnus, crossing 

 the direction of its fibres, and is expended in its substance, sending regularly- 

 arranged ramifications upwards and downwards. 



This is the respii-atory nerve of Bell. 



4. Pectoral or Inferior Thoracic Branches. 



Five principal are distinguished : 



1. One emanating from the sixth and seventh cervical pairs, particularly 

 the former, and passing to the internal face of the sterno-prescapularis (or 

 pectoralis), to ramify exclusively among its fibres, after dividing into two 

 branches : an anterior, short and thick, and a posterior, long and slender 

 (Pig. 347, 10). 



2. A second branch, arising from the anterior brachial and cubito-plantar, 

 or median nerves, by two roots, which join in forming an arch beneath the 

 maxillary artery. 



It passes between the two portions of the deep pectoral muscle, and 

 terminates in the superficial one, after furnishing some ramuscules to the 

 pectoralis magnus by means of a long thin filament which is carried back 

 to the external surface of that muscle (Fig. 347, 11). 



3. The other three, destined to the pectoralis magnus, generally come 

 from the trunk that constitutes the subcutaneous thoracic branch. Com- 

 prised between the serratus magnus, and pectoralis magnus, they are 

 directed downward and backward, and enter the latter muscle. One of them, 

 longer and thicker than the other, follows the course of the spur vein. 



5 Subcutaneous Thoracic Branch. (Fig. 347, 9.) 



This is a very remarkable nerve, arising from the brachial plexus by a 

 trunk common to it and the ulnar nerve. Placed at first to the inside of that 

 nerve, it soon leaves it to pass backward to the internal face of the caput 

 magnum and the panniculus carnosus. In its long course, it acts as a 

 satellite to the spur vein, above which it is situated. It may be followed 

 to the flank, where its terminal divisions are lost in the substance of the 

 subcutaneous muscle. Those it gives off are also destined to that muscle ; 

 they anastomose with the majority of the perforating intercostal nerves, 

 forming an elaborate network on the inner face of the panniculus. 



One of its branches, along with a voluminous perforating nerve, 

 bends round the inferior border of the latissimus dorsi, and passes forward 

 to enter the scapulo-humeral portion of the subcutaneous muscle. 



