THE R. LATERALIS ACCESSORIUS. 205 



greater than the number of nerves which penetrate the 

 cranium. The dorsal surface does not present superficial 

 organs in regions other than this one. 



The three meningeal nerves just described as roots of 

 the r, lateralis accessorius all have intra-cranial origins 

 and pursue essentially similar courses. They are, more- 

 over, all bound together in an intricate and more or less 

 variable plexus. There are farther cephalad two menin- 

 geal nerves which have extra-cranial origins from the 

 supra-orbital trunk and which do not enter this plexus 

 but are destined chiefly, at least, for the skin of the top 

 of the head farther cephalad. I regard them as primarily 

 general cutaneous nerves and as such have described them 

 in the preceding pages. They are, however, doubtless 

 accompanied by sympathetic or other visceral fibres and 

 they may participate somewhat in the general meningeal 

 plexus. Indeed the whole plexus is vastly more compli- 

 cated than my diagrams indicate, and only the larger 

 nerves could be traced with precision. 



These organs overlying the optic lobes, which I have 

 assumed to be terminal buds, are structurally similar to 

 those about the nasal apertures, which I regard as pit- 

 organs. The nerve supply here also is not absolutely free 

 from ambiguity, and I must admit the possibility that 

 these fibres are derived from the lateralis roots by an 

 intra-cranial anastomosis which I have overlooked. 



Almost directly dorsad of the origin of the first root of 

 the r. lateralis accessorius and after receiving fibres from 

 the other roots, which vary in number and importance in 

 different individuals, the main r. lateralis accessorius 

 turns abruptly caudad, first, however, receiving the anas- 

 tomosing fibres from the most cephalic twig of the r. 

 supra-temporalis vagi, as described under that nerve. It 

 runs closely appressed to the outer surface of the cranium 

 not far from the median line and contains very small 

 fibres with a few of slightly larger calibre which are much 



