510 NERVES OF THE NECK. 



num. and joins the other divisions of the eighth pair, 

 along with which, and enclosed in the same sheath, it 

 passes through the foramen lacerum posticus, and thence 

 to the muscles on the side of the neck. 



In the foramen lacerum it is connected to the vagus by 

 one or more filaments. On the outside of the foramen it 

 divides itself into two branches internal and external. The 

 former is the smaller and joins the pneumogastric, while 

 the external is the continuation of the accessory nerve, 

 which proceeds outward, behind the internal jugular vein, 

 to the sterno-mastoid muscle, the upper third of which it 

 perforates and supplies with filaments, anastomosing with 

 the second, third, and fourth cervical nerves, and finally 

 being distributed upon the trapezius as low down as the 

 scapula. 



The function of this nerve is regarded as purely motor, 

 though the observations of Todd and Bowman assign sen- 

 sation to the fibres of the internal branch. This nerve, 

 along with the pneumogastric, has been compared to a com- 

 pound or spinal nerve, the spinal accessory being the motor, 

 while the vagus, with its ganglia, represents the sensory. 



TJie lingual, liypoglossal, or ninth pair of nerves, (Fig. 91.) 

 This nerve is the motor nerve to the tongue, as well as to 

 several structures at the superior part of the neck. It 

 arises from the medulla oblongata between the corpus pyr- 

 amidale and corpus olivare, by six or ten filaments, which, 

 uniting together, pass out of the cranium through the an- 

 terior condyloid foramen of the occipital bone. It then 

 proceeds forward, between the internal jugular vein, and 

 internal carotid artery, ascending with the vein as low as 

 the angle of the jaw, when it curves across the occipital 

 branch of the external carotid, taking the course of the 

 digastric muscle and lingual artery, to the base of the 

 tongue above the os-hyoides ; here it passes above the 

 mylo-lm)ides, crossing the hyo-glossus, and dividing into 

 filaments which supply these muscles, the genio-hyo-glos- 

 sus and the lingualis, and continued forward through the 

 tongue as far as its tip. 



