THE SPINAL ACCESSORY NERVE 



809 



The meduUary part arises from the lateral aspect of the medulla by several 

 rootlets which are behind and in series with those of the vagus (Fig. 629). The 

 spinal part arises from the cervical part of the spinal cord by a series of fasciculi 

 which emerge between the dorsal and ventral roots. The bundles unite to form 

 a trunk which is very small at its origin at the fifth segment of the cord, but 

 mcreases m size when traced toward the brain, since it continually receives accessions 

 of hbers. It passes through the foramen magnum and joins the medullary part. 



Fig. 650. — Neck of Horse, After Removal of Part of Cutaneus and Trapezius. 

 a, a', Brachiocephalicua; b, anterior superficial pectoral muscle; c, cervical cutaneus; d, sterno-cephalicus; e, 

 omo-hyoideus; /, sterno-thyro-hyoideus; g, trachea; h, k', h" , tendons of splenius, brachiocephalicus, and longissimus 

 atlantia; i, trapezius cervicalis; h, supraspinatus; I, anterior deep pectoral muscle; m, rhomboideus cervicalis; 

 n, serratus cervlcis; o, splenius, upper and lower borders of which are indicated by dotted lines; -p, parotid gland; 

 g, parotido-auricularis muscle; r, wing of atlas; s, spine of scapula; 1, external maxillary yein; 2, S, jugular vein; 

 4, carotid artery ; 5, descending branch of inferior cervical artery ; 6, cephalic vein ; 7-1 1 , ventral branches of second to 

 seventh cervical nerves; 12, cutaneous branch of second cervical nerve; 13, cervical branch of facial nerve^ 14, terminal 

 branches of dorsal divisions of cervical nerves; 15, dorsal branch of spinal accessory nerve. (After EUenberger-Baum, 

 Top. Anat. d. Pferdes.) 



The trunk thus formed sends its medullary fibers to the vagus and glosso-pharyngeal 

 nerves and emerges through the foramen lacerum posterius. It then runs backward 

 and downward with the vagus in a fold of the guttural pouch, separates from that 

 nerve, crosses the deep face of the mandibular gland and the occipital artery, and 

 divides in the recessus atlantis into dorsal and ventral branches. 



It is connected by anastomotic branches with the vagus and hypoglossal nerves and the 

 anterior cervical ganglion of the sympathetic, and contributes a branch to the pharyngeal plexus. 



