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figs. 3, 4) and in certain Teleosts (Allis 1909a, pp. 82—83), as the canal in question is 
too narrow to be able to contain, in addition to r. ophthalmicus profundus, the presumably 
rather powerful oculomotorius nerve as well, and moreover, as we have seen in my 
account above, there is found a special foramen (III) which can only be related to 
this last-mentioned nerve. 
From a small incisur ( ophth. lat, text fig. 62, 63 C; PI. 21, fig. 2) on the posterior 
margin of the sphenoid dorsally of the trigeminus incisur a shallow furrow {ophth. lat. 
PI. 22, fig. 3 ) extends in a rostral direction. Straight above the outer opening of the 
profundus canal, between it and the corner a h this furrow proceeds through the aperture 
ophthal. l'at lt into a canal that continues in a rostro-dorsal direction to a position below 
and somewhat behind the corner a, where it has its anterior opening {ophth. lat 3 , text 
figs. 61, 63 A, B; PL 21, figs, i, 3 ). The position of the canal in the sphenoid is shown in 
text fig. 64 B (ophth. lat). In a dorsal direction there issues from this canal another one 
of finer calibre, which opens on the latero-dorsal surface of the pars lateralis (r, text 
fig. 63 A; PI. 21, figs. 2, 3 ) in the present state of preservation of the cranium. Originally, 
however, this finer canal has continued in a dorsal direction through the cartilage that 
was attached to this surface and has consequently had its exit on the dorsal surface of 
this cartilage, immediately beneath the membrane bones of the cranial roof. 
The fairly coarse canal, ophth. lat, now described has, as far as can be understood, 
been pierced by the n. ophthalmicus lateralis (perhaps by ophthalmicus trigemini as well) 
and the shallow furrow leading to the small incisur on the process b may also have 
been developed in relation to the same nerve (cf. Gegenbaur 1872, pp. 67—69; yan Wijhe 
1882, pp. 229—23o). The fine canal that proceeds in a dorsal direction from the ophthal¬ 
micus lateralis canal may have contained some nerve branch to the supraorbital canal, 
and it is not impossible that vessels have also passed through it. This seems to be sup¬ 
ported by the fact that the foramen v 2 forms the ventral opening of a canal that pro¬ 
ceeds dorsally and probably opens into the ophthalmicus lateralis canal about opposite 
the fine canal r just mentioned issuing from the dorsal side in an upward direction. 
The abducens nerve was probably transmitted through the incisure fi described 
above (text fig. 63 A, B, C; PL 21, figs. 1— 3 ; Pl. 22, fig. 3 ). For this incisure seems to 
have been situated slightly in front of the place where n. abducens must have left me¬ 
dulla oblongata, and it is also in the right position in relation to the suppossed place of 
origin of m. rectus externus (fossa my). N. abducens would thus have had a short 
straight course in a rostro-lateral direction as in Teleosts. That it cannot have had its 
exit together with or in close connection with the trigeminus branches as in certain 
other recent fish forms (Gegenbaur 1872, p. 73; Allis 1902, pp. i 32 — 133 ; Veit 1907, 
p. 188; Lehn 1918, pp. 372, 3 gi) seems to be shown by the fact that in such a case it 
would first have had to turn off in a dorsal direction to arrive at the trigeminus exit 
situated high above the floor of the cranial cavity and then to reach m. rectus externus 
in a ventral direction. 
As has been pointed out above, the n. facialis has pierced the anterior cartilaginous 
part of the labyrinth region. In the description of the myodome and the trigemino-faci- 
alis chamber below I shall have an opportunity to enter in more detail upon the question 
of its course through the cranial wall, and in this connection I may therefore confine 
