TRIASSIC FISHES FROM SPITSBERGEN 
161 
opisthotic and the supratemporo-intertemporal, of which something has been indicated 
above, I may refer to the description below of the membrane bones of the cranial roof. 
The above-mentioned (p. 153 ) paired cartilage bone in the postorbital process of 
B. mougeoti apparently represents the autosphenotic ( Ausph , text figs. 61, 64 A, PI. 22, 
figs. i, 3 ). Its length is about 2 I / 2 times as great as its minimum breadth and its two 
ends are blunt. The posterior 
end and the medial margin 
have been joined with cartilage 
in the way shown in text 
figs. 61 and 64 A. 
The cartilaginous part 
in the anterior portion of the 
labyrinth region has been 
pierced by n. facialis (VII, 
text figs. 61, 62; PI. 20, fig. 6; 
PI. 22, figs. 1, 3 ), and prob¬ 
ably by the spiracular canal 
as well, if this was developed. 
Farthest anteriorly this car¬ 
tilage forms the posterior 
boundary of the foramen 
through which the trigemi¬ 
nus roots had their exit (V, 
text figs. 61, 62; PI. 20, fig. 6; 
PI. 21, fig. 3 ). Moreover the 
hyomandibula must apparent¬ 
ly have articulated with the 
same cartilage at least to some 
extent. The places of exit for 
trigeminus and facialis are de¬ 
scribed in detail below. 
The actual boundary 
between the orbitotemporal 
and the labyrinth regions is, 
as usual, not sharp. The auto¬ 
sphenotic extends dorsally a 
long way forward over the orbit and has been attached medially (text figs. 61, 64 A), to 
cartilage that passes over into the interorbital wall. This cartilage (ca, text fig. 61), which 
was situated immediately beneath the dermal bones of the cranial roof certainly grew 
thinner rostrally. While the boundary in the dorsal parts of the cranium is thus found 
far forward, in the middle and ventral parts, on the other hand, it is situated consider¬ 
ably more backwards. For reasons that will be given below most ventrally it ought 
really to be drawn through the postero-ventral parts of the large ossification that 
occurs in the orbito-temporal region, but for practical reasons I have here in my 
Stensio, Triassic Fishes from Spitzbergen. 21 
Text fig. 6i« Birger ia mougeoti Agassiz. 
The neurocranium from the ventral side. After P. i65. ?/ 4 . The cartilaginous parts 
are dotted, 
Ausph, autosphenotic; Pro. o, prootico-opisthotic, including the epiotic as well; 
Psph, parasphenoid; S plien. sphenoid; a, corner on the edge between the latero- 
dorsal and lateral (ventro-lateral) surfaces of the sphenoid; ca, cartilage joining 
the autosphenotic with the latero-dorsal surface of the sphenoid; my. trig , open¬ 
ing of the myodome and trigemino-facialis chamber; bphth. lat 2 , anterior opening 
of the canal for n. ophthalmicus lateralis; pr. asc, processus ascendens of the 
parasphenoid; t, nerve or blood vessel foramen; vl, ventral lamella from the 
supratemporo-intertemporal; vp, ventral process from the supratemporo-inter¬ 
temporal ; v 3 , vs, foramina presumably for vessels and nerves to the cranial 
roof; VII, the posterior opening of the facialis canal; IX, foramen for n. glosso- ■ 
pharyngeus. 
