168 ERIK A : SON STENSIO 
From what has been said it thus seems evident that, apart from possibly existing 
fontanels, the roof of the primordial neurocranium between the two partes laterales 
consisted of cartilage. As we shall see, a fontanel is found in the Saurichthyids, in 
which it extends from the labyrinth region into the most posterior part of the orbito¬ 
temporal region (cf. Part II). 
The cranial cavity continues forwards through the whole sphenoid and even in the anterior 
part of this bone it still seems to have had a fairly considerable size. Text fig. 64 A, B 
shows the conditions in a 
transverse section in the 
middle and posterior part of 
this bone. 
From the forward ex¬ 
tension just described of the 
cranial cavity it ought to be 
evident that n. olfactorius 
had an intracranial course 
(right) until it reached the 
nasal capsule. 
The foramen opticum 
(II, text figs. 62, 63 A, B, C; 
PI. 20, fig. 6; PI. 21, figs. 1 
— 3 ; PI. 22, figs. 1, 3 ) is situ¬ 
ated not far above the pos¬ 
terior end of the fenestra op¬ 
tica (fen. opt.) and thus has 
its normal position. Imme¬ 
diately in front of it there 
is another smaller foramen, 
which has probably been,, 
pierced by some vessel, the 
most probable one being ar- 
teria optica (a. retinalis, 
Danforth, 1912, p. 443; cf. also Allis, 1897a, pp. 498—499; 1908a, p. 223 ; 1908b, 
pp.258—262; 1909a, p. 186; 1911, p. 290; 1912, pp. 119—120; Allen 1905, pp. 56—57). 
N. oculomotorius (III, text figs. 62, 63 A, B, C; PI. 20, fig. 6; PI. 21, figs. 2, 3 ; PL 22, 
fig. 3 ) apparently had its exit in the orbit through a foramen a short distance behind 
the for. opticum and slightly higher than this. 
High up dorsally and somewhat rostrally of the latter foramen there are three 
foramina in a group (IV, v 2 , v 4 , text fig. 62, 63 A, B, C; PI. 20, fig. 6; PI. 21, figs. 1— 3 ; 
PI. 22, figs. 1, 3 ). The most posterior of them fp g ) does not lead into the cranial cavity 
but into a canal that pierces the pars lateralis of the sphenoid in a dorsal direction. 
The two others form the outer exit of two canals, situated close together, which pierce 
the pars lateralis in a postero-medial direction and consequently have their inner openings 
situated somewhat caudally of their outer ones. One of these two canals must have been 
Psph bsph 
Text fig. 64. Birgeria mougeoti Agassiz. 
Cross-section through the orbitotemporal region. After P. 16S. 
The cartilaginous parts are dotted. 
A) through the middle part of the orbitotemporal region. 
B) through the posterior part of the same region. 
Ausph, autosphenotic; Dsph, dermosphenotic; Fr, frontal; Psph, parasplienoid; Spli, 
sphenoid; Stemp.it, supratemporo-intertemporal; bp, basipterygoid process; bsph, 
portion of the pars basalis of the sphenoid between fenestra optica and canalis 
transversus; cv, cranial cavity; fen. opt, fenestra optica; my v myodome portion, of 
the postorbital cavity; oplith. lot, canal for r. ophthalmicus lateralis, pd, process on 
the medial side of the' parasphenoid probably indicating the position of the homologue 
of the alisphenoid pedicle oiAntia; pr. asc, processus ascendens of the parasphenoid; 
trig. fac. cli, portion of the postorbital cavity, corresponding to a trigemino-facialis 
chamber; vl, ventral lamella from the supratemporo-intertemporal. 
