. The anatomy of the human body. Human anatomy; Anatomy. THE BRACHIAL PLEXUS. 781 with the spinal accessory, between the cervical fasciculi of the splenius and the sterno- mastoid. Also, a branch for the trapezius, which arises from the third nerve, passes obliquely downward and backward to the deep surface of the muscle, and anastomoses with the spinal accessory of Willis, which it re-enforces, and with which it may be traced as far as the lower angle of the muscle. Lastly, the branches for the levator anguli scapula and the rho7nboideus; these are rath- er small branches, which arise from th
. The anatomy of the human body. Human anatomy; Anatomy. THE BRACHIAL PLEXUS. 781 with the spinal accessory, between the cervical fasciculi of the splenius and the sterno- mastoid. Also, a branch for the trapezius, which arises from the third nerve, passes obliquely downward and backward to the deep surface of the muscle, and anastomoses with the spinal accessory of Willis, which it re-enforces, and with which it may be traced as far as the lower angle of the muscle. Lastly, the branches for the levator anguli scapula and the rho7nboideus; these are rath- er small branches, which arise from the back part of the third and fourth cervical nerves, as they emerge from between the transverse processes of the vertebrae, pass obliquely downward and backward, turn round the scalenus posticus in contact with it, and are distributed to the levator anguli scapula; and the upper part of the rhomboideus. The same branches appear to supply both muscles. The Anterior Branches of the Fifth, Sixth, Seventh, and Eighth Cervical AND First Dorsal Nerves. These branches are remarkable for their size, in which respect they surpass the pre- ceding, and are almost all equal. On emerging from the inter-vertebral foramina, they come into relation with the two scaleni muscles, which are separated from each other, and sometimes are perforated by them; they give off some very slender filaments to these muscles, and, converging, anastomose together so as to form the brachial plexus, from which all the nerves of the upper extremity are derived. The Brachial Plexus. • ' The brachial plexus {h, fig. 268) extends obliquely from the lateral and inferior part of the neck to the cavity of the axilla, or, rather, to the inner side of the head of the hume- rus, where it terminates by dividing into the nerves of the upper extremity ; it is formed in the following manner : The fifth and sixth cervical nerves (5, 6, fig. 286) unite at a short distance from the scaleni, and the cord thus formed passes very
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