TRIASSIC FISHES FROM SPITZBERGEN 
169 
pierced by n. trochlearis, and as this nerve is always rather narrow, it does not seem 
improbable that it was the smaller one (IV). The anterior and larger one (v 4 ) seems to 
have transmitted a vessel and its position seems to suggest that this vessel was v. cere¬ 
bralis anterior. 
In Elasmobranchs this vein is developed (Rex 1891, PL 25, fig. 10; PI. 26, fig. 21; 
Burckhardt 1907, PI. 3, fig. 5; Allis 1902, PI. 12, fig. 6; O’ Donoghue 1914, pp. 439—440; 
T. J. Parker 1887, p. 712). In Amia Allis (1897a, PI. XXI, figs. 9, 10, 11; 1909a, p. 3g) 
found it and, according to his statements (1909a, p. 187), it is also found in Lepidosteus and 
Teleosts (1909a, p. 3g; p.207). 1 ) In Polypterus Lehn (19x8, p. 38o, figs. 3, 4) has found 
two vein foramina in the neighbourhood of for. trochlearis, one of which is situated 
caudally, the other dorsally of the nerve foramen mentioned. Lehn does not give any 
detailed description of the veins that passed through these foramina and it is therefore 
uncertain which of them transmitted the v. cerebralis anterior. 
Allis (1909a, pp. 51—55) has described in certain Teleosts a fine arterial branch 
that pierces the alisphenoid, and, according to Demme (i860, p. 10) in Accipenser ruthenus 
a couple of small rami perforantes are sent off from art. carotis externa during its for¬ 
ward course «an der inneren Wand der Schlafen und Augenhohle». I have been unable 
to establish whether any foramen for such a branch was present in the sphenoid of 
B. mongeoti. In any case it seems to me highly improbable, however, that the foramen (v 4 ), 
should have transmitted such an arterial branch instead of the vena cerebralis anterior. 
The place of exit for the trigeminal roots in B. mougeoti was, as already shown by 
my account above, situated on the boundary between the sphenoid and the anterior 
cartilaginous part of the labyrinth region. It appears accordingly, in the present state 
of preservation of the cranium, only as a considerable incisur (V) on the posterior margin 
of the sphenoid between the two processes b and c (text figs. 62, 63 A, B, C; PI. 20, 
fig. 6 ; PI. 21, figs. 1, 3 ; PI. 22, figs. 1— 3 ). 
In the anterior boundary of the trigeminus incisur on the sphenoid we find 
the posterior opening (V u , text fig. 63 C) of a fine canal (Fj, text fig. 62) which 
passes off forwards and somewhat laterally. The anterior opening of this canal (V Ie , text 
fig. 63 A, B; PI. 21, figs. 1, 3 ) is situated about half way between the anterior boundary 
of the trigeminus incisur and the foramen oculomotorii (III) and is divided by an in¬ 
complete septum into a dorsal and a ventral part. As is shown by comparisons with 
recent Elasmobranchs, Ganoids and Teleosts, it cannot in this case be anything but the 
canal for r. ophthalmicus profundus or a nerve fairly equivalent to this. It is difficult 
to say with certainty what is the signification of the division of the external opening 
of the canal into two parts. It may of course be connected with a bifurcation of the 
ophthalmicus profundus itself into two branches and, on the other hand, it is not incon¬ 
ceivable that it may be caused by some vein corresponding to v. encephalica of the 
Teleostei (Allis 1909 a, pp. 44, 48; Allen 1905, pp. 84—85; PI. Ill, fig. 24), which has left 
the cranial cavity together with r. ophthalmicus profundus. I consider it impossible that 
n. oculomotorius should have had its exit this way as in Polypterus (Traquair 1871, 
p. 170; PI. VI, fig. 3 ; Pollard 1892a, pp. 394—395; PI. 28, fig. 12; Lehn 1918, p. 38 o, 
*) The same vein is also noticed in Lepidosteus by Veit 1907, p. 193. 
Stensio, Triassic Fishes from Spitzbergen. 22 
