366 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



separated from it, and is always lateral to it in position. It immedi- 

 ately enters the rectus externus on the posterior margin of that 

 muscle. 



BRANCHES OF THE TRIGEMINUS GROUP. 



The ramus lateralis trigemini leaves the skull by the foramen in 

 the supraoccipital, and courses backwards near the middle line be- 

 tween the lateral musculature, and that of the interspinous bones. 

 It is reinforced immediately after leaving the skull by the important 

 dorsal branches of the first, second and third spinal nerves, and acts 

 as a collector for slenderer branches from all the other rami dorsales^ 

 (Figs. 6, 14, 15, PL IV.) 



The ramus oticus emerges from its foramen in the sphenotic and 

 supplies the mucous canal running backwards and forwards from this 

 point. Two short cutaneous branches penetrate vertically the adduc- 

 tor mandibular near its dorsal line of origin for the skin overlying 

 that and a larger posterior branch runs through the fibres of the 

 adductor mandibular to become superficial over the levator operculi. 

 The mucous canal in the preoperculum is supplied in its upper part 

 by a descending branch, which runs underneath the adductor mandi- 

 bular and on the surface of the dilatator operculi to become super- 

 ficial at the posterior edge of the former muscle. The ramus oticus 

 thus contains ordinary sensory fibres in addition to those destined for 

 the mucous canals. 



The ramus ophthalmicus superficialis emerges from the skull 

 through a canal which is considerably lai'ger than, and lies dorsally 

 from that through which the R. opht. profundus emerges. It gains; 

 the orbit immediately under the osseous roof of which it lies, and 

 escapes from it on to the upper surface of the skull through a foramen 

 above that through which the proj undus passes. In its course to the 

 mucous canals in the neighbourhood of the nasal sacs it crosses super- 

 ficially to the outside of the profundus, but does not communicate 

 with it. In the orbit it is separated from the profundus by the 

 oi'igin of the dilatator operculi. 



The ramus ophthalmicus profundus follows the course implied 

 above through the orbit, gives off a slender branch to join the ramus 

 ciliaris, another to the skin and fat in front of the eye and along the 

 outer border of the nasal sac. Immediately after reaching the upper- 



