Dissection of Sheep^s Head. 251 



The Hypo-glossal is a motor nerve ; after passing from the 

 cranium by the condyloid foramen, it crosses first the Yagus 

 (being embraced between it and the spinal branch of the 

 Spinal Accessory), and then the carotid artery; near this 

 point it gives off a branch, the descendens noni, which de- 

 scends in the sheath of the carotid artery, and is distributed 

 to the depressor muscle of the os hyoides. The further pro- 

 longation of the main stem of the Hypo-glossal to its disap- 

 pearance beneath the mylo-hyoid muscle has been traced in a 

 previous dissection (p. 231). 



The Spinal Accessory is a motor nerve ; its origin from the 

 cervical portion of the spinal cord, and entrance into the 

 cranium by the foramen magnum was noted above : 

 after leaving the cranium through the foramen lacerum it 

 divides, the Accessory part gives twigs to the Yagus, and the 

 Spinal part continues backwards under the superior extremity 

 of the submaxillary gland, passes down the neck, supplies 

 the Sterno-mastoid muscle, and is lost in the Trapezius muscle. 



The Pneumogastric or Vagus is a mixed nerve, originating 

 by motor and sensory roots, and is the largest of the cranial 

 nerves in the neck. In its passage through the foramen 

 lacerum in the same sheath of dura mater with the Spinal 

 Accessory, it has developed a distinct ganglion, termed the 

 ganglion of the root ; and after it has escaped from the foramen, 

 and received the Accessory part of the Spinal Accessory, it 

 presents a second and fuller enlargement, termed the ganglion 

 of the trunk : it then descends behind the guttural pouch, and 

 proceeds down the neck in the same sheath with the common 

 carotid artery.* The principal branches in the upper part of 

 its course, near the head, are two, mz., (1) a Pharyngeal 

 branch, which comes off near the ganglion of the trunk and 



* The further course of this nerve has been previously seen in the dissection 

 of the Rat. 



