80 THE NERVOUS SYSTEM OF THE FROG 



close alongside the skull wall t between it and the eyeball. Trace 

 it forwards to the nose. 



ii. The ramus maxillo-mandibularis runs directly 

 outwards behind the eyeball, in front of the 

 auditory capsule and between the temporal and 

 pterygoid muscles. After a very short course it 

 divides into the maxillary and mandibular nerves. 

 To trace this nerve and its branches remove the squamosal bone 

 carefully, and find the nerve lying on the pterygoid muscle and 

 immediately behind the eye. Follow the nerve behind thepterygoid 

 and temporal muscles to the skull, removing the muscles if neces- 

 sary ; and then trace the branches outwards to their distribution. 

 a. The ramus maxillaris runs forwards and out- 

 wards in the floor of the orbit, behind and 

 below the eyeball, to the margin of the upper 

 jaw, which it reaches about midway along 

 its length : it then ends in branches which 

 run along the jaw, some forwards and some 

 backwards, supplying the upper lip, the lower 

 eyelid, and other neighbouring parts. 

 /3. The ramus mandibularis runs parallel to 

 and behind the ramus maxillaris as far as 

 the outer border of the eyeball, giving 

 branches to the temporal and pterygoid 

 muscles : it then turns backwards, outwards, 

 and downwards, and passing across the inner 

 side of the upper jaw, reaches the outer 

 surface of the mandible just behind the 

 insertion of the temporal muscle : it then 

 runs forwards along the outer side of the 

 lower jaw to the chin, supplying the lower 

 lip and the muscles of the floor of the mouth. 

 6. The abducens is a very slender nerve which arises from 

 the ventral surface of the medulla close to the median 

 line, and a short way behind the pituitary body. It 

 passes either through, or in very close contact with, the 

 Gasserian ganglion, and entering the orbit supplies the 

 retractor bulbi and the rectus externus muscles. 

 The abducens nerve is too small to be made out satisfactorily 

 in the frog. 



