CEREBRO-SPINAL NERVES 397 



it gradually becomes thicker by the addition of fresh fibres from the cord, 

 and enters the cranium through the foramen magnum. It receives some 

 fibres from the posterior part of the medulla oblongata, and then, united 

 with the pneumogastric for about an inch of its course, passes out through 

 the foramen lacerum basis cranii. Beyond this point the nerve is directed 

 backward beneath the mastoido-humeralis muscle, giving branches to the 

 superior cervical ganglion, the sterno-maxillaris, the mastoido-humeralis, 

 and finally terminates in the cervical and dorsal trapezius. 



It is a nerve of motion. 



Twelfth, Hypoglossal. — l»riginating from the posterior part of the 

 medulla oblongata the hypoglossal nerve leaves the cranium through the 

 anterior condyloid foramen and descends between the pneumogastric and 

 spinal accessory nerves on the exterior face of the guttural pouch. Passing 

 over the side of the pharynx and larynx it is continued onwards beneath 

 the mylo-hyoid and hyo-glossus brevis muscles, and distributed to all the 

 muscles of the tongue. 



Soon after leaving the anterior condyloid foramen the hypoglossal 

 nerve receives a considerable twig from the inferior branch of the first 

 cervical pair, and it is further connected with the superior cervical ganglion 

 on the outer part of the guttural pouch. 



It is a motor nerve, and excites contraction of the muscles of the 

 tongue during feeding or whenever they are required to move. 



SPINAL NERVES 



These nerves differ from those last described, in the fact that each of 

 them arises from the side of the spinal cord by two roots — one sensitive, 

 the other motor. The sensitive root is the upper one and has upon it a 

 ganglion. The motor root is the one below. They pass out of the spinal 

 canal together through the intervertebral opening, and then the two roots 

 join their fibres to form a compound nerve, a nerve having motor and 

 sentient properties. Each spinal nerve now divides into a superior and 

 inferior division, and from the latter sends a branch to the sympathetic. 



Cervical Nerves. — Of these there are eight pairs. The first cervical 

 nerve leaves the spinal canal through the antero-internal foramen of the 

 atlas. The superior branches accompany the occipital artery and vein to 

 between the rectus capitis posticus and the obliquus capitis superior. At 

 its origin it gives branches to the small muscles about the poll. The 

 inferior branch passes downwards and is distributed to the thyro-hyoid, 

 subscapulo-hyoid, sterno-thyroid, and sterno-hyoid muscles. It sends a 

 small branch to the hypoglossal nerve, and another to the superior cer- 



