THE BEACHIAL PLEXUS. 755 



by its posterior border, and corresponds inwardly to the vertebral artery and 

 vein, as well as to the nervous vertebral filament proceeding to the sympathetic, 

 and accompanying these vessels. 



Mode of distribution. Immediately after leaving the interspace in the 

 scalenus, the brachial plexus arrives beneath the shoulder, near the scapulo- 

 humeral angle. There it divides into a certain number of branches, amongst 

 which it is impossible to distinguish the terminal divisions and collateral 

 ramuscules. Without noticing this distinction, however, we will describe 

 them in succession, commencing with those that pass to the trunk, and after- 

 wards those which are destined for the limb. The latter will be examined 

 in the following order : first, the shortest, or those which proceed to the 

 upper parts of the member, and next, the longest branches, or those passing 

 to the foot. 



All these divisions are named and classified in the following enumera- 

 tion : 



1. Diaphragmatic branches. 



2. Angularis and rhomboideal branch. 



3. Serratus magnus or superior thoracic branch. 



4. Pectoral or inferior thoracic branches. 



5. Subcutaneous thoracic branch. 



6. Latissimus dorsi or great dorsal branch. 



7. Axillary nerve. 



8. Adductor brachii or teres major brandies. 



9. Subscapular branches. 



10. Super scapular nerve. 



11. Anterior brachial or musculo-cutaneous nerve. 



12. Radial nerve. 



13. Ulnar or cubito-cutaneous nerve. 



14. Median or cubito-plantar nerve. 



PREPARATION OF THE BRACHIAL PLEXUS. The animal is placed in the first position, and 

 slightly inclined to one side by allowing one of the anterior limbs to hang un- 

 restrained. The pectoral muscles are then excised close to their insertion in the unfixed 

 limb, and turned upwards, maintaining them in this position by the chain tentacula 

 which are detached superiorly to a band that unites the extremities of the two 

 suspensory diagonal bars. Care should be taken to separate the pectoralis magnus from 

 the panniculis, in allowing the latter to fall on the table along with the limb. By tear- 

 ing through the considerable mass of cellular tissue surrounding the nerves of the 

 brachial plexus, these soon appear, and may be isolated with the greatest facility. It is 

 advisable in this dissection to preserve the arteries ; and it is also of importance to leave 

 the perforating intercostal branches intact, in order to observe the anastomoses of these 

 with the subcutaneous thoracic division. 



In this operation, the anterior limb is very much separated from the trunk, and the 

 relations of the nerves are necessarily more or less changed ; but it exhibits the whole of 

 the plexus in the most perfect manner. 



To trace the divisions of the principal nerves from this plexus, a limb entirely 

 removed from the body is made use of, and, if possible, with the arteries injected. The 

 nerves are then found in their natural relations, and can be more readily dissected. 

 Figures 347, 348 will guide the student in looking for these nervous divisions. 



1. Diaphragmatic Branches. 

 See the description of the diaphragmatic nerve above. 



2. The Angularis and Ehomboideal Branch. (Fig. 347, 7.) 



Entirely furnished by the sixth cervical pair, this branch is directed 

 upwards to the surface of the angularis (anterior portion of the serratus 



