THE ELEVENTH OR SPINAL ACCESSORY NERVE 



691 



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 in- 

 creases 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. 

 The trunk thus formed sends its medullary fibers to the tenth and ninth nerves and 

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



FiG. 518. — Neck of Horse, after Removal of Part of Pannicttltts and Trapezitts. 

 a, a', Mastoido-humeralis; b, anterior superficial pectoral muscle; c, cervical panniculus; d, sterno-cephal- 

 icus; c, omo-hyoideus; /, sterno-thyro-hyoideus; g, trachea; h, h' , h", tendons of splenius, mastoido-humeralis, 

 and trachelo-mastoideus; /, trapezius cervicalis; k, supraspinatus; I, anterior deep pectoral muscle; m, rhomboideus 

 cer\-icalis; n, serratus cervicis; o, splenius, upper and lower borders of which are indicated by dotted Unes; p, parotid 

 gland; q, parotido-auricularis muscle; r. wing of atlas; s. spine of scapula; 1, external maxillary vein; 3, 3, 

 jugular vein; 4, carotid artery; 5, descending branch of inferior cervical artery; ff, cephalic vein; 7-ii, ventral 

 branches of second to seventh cervical nerves; 1^, cutaneous branch of second cervical nerve; 13, cervical branch 

 of facial ner\-e; 14, terminal branches of dorsal divisions of cer^•ical nerves; 15, dorsal branch of spinal accessory 

 nerve. (After EUenberger-Baum, Top. Anat. d. Pferdes.) 



ward with the vagus in a fold of the guttural pouch, separates from that nerve, 

 crosses the deep face of the submaxillary 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 

 superior cervical gangUon of the sympathetic, and contributes a branch to the pharyngeal plexus. 



The dorsal branch (R. dorsalis) (Figs. 433, 517, 518) receives a twig from the 

 second and third cervical nerves and turns around the atlantal tendon of the splenius 



