BRACHIAL PLEXUS. 



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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 unrestrained. The 

 pectoral muscles are then excised cloae to their insertion in the unfixed limb, and turned 

 upwards, maintaining them in this position by the chain tentacula which are attached 

 superiorly to a band that unites the extremities of the two suspensory diagonal bars. Care 

 should be taken to separate the pectoralia magnus from the panniculis, in allowing the latter 

 to fall on the table along with the limb. By tearing through the considerable mass of con- 

 nective 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 branchea intact, in order to 

 observe the anastomoses of these with the subcutaneous thoracic division. 



In this operation, the anterior limb is very mucii 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 tiiis plexus, a limb entirely removed 

 from the body ia made uae of, and, if possible, with the arteries injected. The nerves are then 

 found in their natural relations, and can be more readily dissected. Figa. 465, 466 will 

 guide the student in looking for these nerve-divisions. 



1. Diaphragmatic Branches. 



See the description of the diaphragmatic nerve above. 



2. The Levator An&uli Scapula and Ehomboideal Branch (Fig. 465, 7). 



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

 to the surface of the levator anguli scapulae. It soon divides into several fila- 

 ments, which are wholly expended in the substance of that muscle, the serratus 

 magnus, and the rhomboideus. The filament supplying the latter is slender 

 and very long, and, to reach its destination, passes through the levator anguli 

 scapulae. 



'4. Serratus Magnus, or Superior Thoracic Branch (Fig. 465, 8). 



This very remarkable branch proceeds, by two principal portions, from the 

 fasciculus common to all the divisions of the brachial plexus — one emanating 

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