THE INFRA-ORBITAL TRUNK. 179 



the order in which they are given off irrespective of the 

 components contained in them. Remembering that the r. 

 buccalis contains all of the lateralis fibres, the r. mandi- 

 bularis V all of the motor and a part of the general 

 cutaneous, and the r. maxillaris the remainder of the 

 general cutaneous, the peripheral relations of each of 

 these nerves can be easily gathered from the plot (Fig. 3). 

 Before taking up the detailed account, emphasis should 

 again be laid upon the fact that the branches of this trunk 

 are enumerated in this way simply as a matter of con- 

 venience in description. The details of the arrangements 

 of these branches and their fusions with each other have 

 no especial morphological significance, but rather seem to 

 be determined by the individual conditions as a matter of 

 mechanical and functional adaptation. The remarkable 

 way in which different nerves have been compacted into 

 the infra-orbital trunk is obviously due to mechanical 

 causes, chiefly to the excessive development of the eyes. 



/. — TJie R. Opercularis V. 



The first branch to be given off from the infra-orbital 

 trunk is the motor nerve already referred to, which arises 

 close to the cranium, passes back a short distance in com- 

 pany with the first recurrent twig from the Gasserian 

 ganglion to the truncus hyomandibularis, separates from 

 this twig, turns outward, crossing transversely the cephalic 

 edge of the hyomandibular bone and then divides into 

 ventral and dorsal branches (Fig. 22) for the m. levator 

 arcus palatini (Fig. 4, in. I. a. p.) and the m. dilator operculi 

 {in. d. op.) respectively. These motor nerves, it appears 

 from Stannius' description of other species in which the 

 truncus divides into its rami before their separation, should 

 be relegated to the r. mandibularis V. 



