346 DISSECTION OF THE RABBIT 



vertically downwards for about half an inch, and 

 then divides into branches distributed to the sterno- 

 mastoid and other muscles. 



The branch to the sterno-mastoid has already been seen 

 (p. 344). Follow this back to its junction with the main stem 

 of the nerve, and then trace this latter up to the base of the 

 skull. 



2. The hypoglossal nerve, the twelfth cranial, is a stout 

 nerve which leaves the skull by the condylar fora- 

 mina, immediately behind the foramen lacerum 

 posterius, and lies at first very close to the pneumo- 

 gastric, glosso-pharyngeal, and spinal accessory 

 nerves. Outside the skull it 'runs downwards and 

 inwards for about half an inch, and then turns 

 forwards, crossing ventral to the carotid artery 

 at its point of division into internal and external 

 carotids. It then runs forwards and inwards,, 

 along the dorsal surface of the stylo-hyoid muscle, 

 and parallel to the posterior cornu of the hyoid, 

 to the base of the tongue, the muscles of which it 

 supplies. 

 The hypoglossal nerve is readily found, where it turns for- 

 wards between the carotid artery and the stylo-hyoid muscle ; 

 and should be followed from this point backwards to the skull, 

 and forwards to the tongue. 



a. The ramus descendens noni is a branch of the hypo- 

 glossal, which arises from the main nerve just 

 before it reaches the carotid artery. It runs 

 back along the outer border of the carotid for 

 about half an inch, giving branches to some of 

 the muscles of the neck. It then crosses the 

 carotid, about the level of the lower border of the 

 thyroid cartilage, and runs back on the sterno- 

 thyroid muscle, to which as well as to the sterno- 

 hyoid it sends branches. 



The descendens noni is readily found crossing the carotid 

 about the point named above, and shoiM then be traced bach- 



