THE SPINAL ACCESSORY NERVE 809 
The medullary 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 
increases in size when traced toward the brain, since it continually receives accessions 
of fibers. It passes through the foramen magnum and joins the medullary part. 
Fic. 650.—Neck or Horse, ArrerR REMOVAL OF PART OF CUTANEUS AND TRAPEZIUS. 
a, a’, Brachiocephalicus; 5, anterior superficial pectoral muscle; c¢, cervical cutaneus; d, sterno-cephalicus; e, 
omo-hyoideus; /, sterno-thyro-hyoideus; g, trachea; h, h’, h’’, tendons of splenius, brachiocephalicus, and longissimus 
atlantis; i, trapezius cervicalis; k, supraspinatus; /, anterior deep pectoral muscle; m, rhomboideus cervicalis; 
m, serratus cervicis; 0, splenius, upper and lower borders of which are indicated by dotted lines; p, parotid gland; 
q, parotido-auricularis muscle; r, wing of atlas; s, spine of scapula; 1, external maxillary vein; 2, 3, jugular vein; 
4, carotid artery; 5, descending branch of inferior cervical artery; 6, cephalic vein; 7-11, 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 Ellenberger-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. 
Tt 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. 
