TRIASSIC FISHES FROM SPITZBERGEN 
17 
myself to a brief orientation with regard to its main portion, the truncus hyoideo- 
mandibularis. 
After having separated from the palatinus portion this truncus must have turned 
off in a caudal direction entering a latero-caudally running canal, which is bounded by 
the prootico-opisthotic, the cartilage anterior of this bone, the processus ascendens of 
the parasphenoid and a process (vp) from the supratemporo-intratemporal. The position 
of the posterior opening (VII) of this canal is seen in text fig. 61 and PI. 22, figs. 1, 3. 
On the sphenoid there occur a few additional foramina for vessels and nerves that 
have not so far been mentioned. The most important of these is the paired foramen 
(a. car . int, text fig. 63 B; PI. 20, fig. 6; PI. 21, figs. 1, 2; PI. 22, figs. 1, 3 ) found on the 
ventral surface of the portion bsph of the pars basalis. Each of these foramina forms 
the ventral opening for a vertically ascending canal, whose dorsal opening (a. car. int, 
text fig. 63 C; PL 21,. fig. 2) is situated rostro-laterally of the fossa hypophyseos just 
behind the foramen opticum of its side. As I shall show in more detail in part II of 
this work, this canal, which is also found in Saurichthys, has been pierced by arteria 
carotis interna (cf. Allis 1897 a, pp. 497—498; 1908a, pp. 222— 223 ; 1908b, pp. 257—258, 
260—262; 1909a, pp. 54, 186; 1909b; 1911, p.290; 1912, pp. 119—120; 1912a, p.489; 
1914a, pp. 228, 238 , 247; Danforth 1912, pp. 442—445; Demme i860, pp. ir—14; Allen 
I 9 ° 5 > PP* 56 — 57; T. J. Parker 1887, p. 694; Veit 1907, p. 189, fig. 3 ; etc.). This artery 
has, as is clearly seen, occupied its usual position. 
Through the foramina v 3 and v 5 (text fig. 63 A, B; PI. 21, figs. 1— 3 ) both of which 
are situated on the border between the latero-dorsal and the lateral surface of the pars 
lateralis of the sphenoid, vessel and nerve branches to the cranial roof may have had 
their course. Foramen Vi on the latero-dorsal surface forms the present dorsal opening 
for the canal of which v 3 is the ventral one. From Vi the canal has undoubtedly continued 
a short distance through cartilage until it reached the cranial roof. 
With regard to the distribution of bone and cartilage in the orbitotemporal region 
in B. mougeoti I refer to the text figs. 61, 62, 64, where I have tried to reconstruct the 
cartilaginous parts. 
A comparison between the orbitotemporal region in B. mougeoti and a number of 
other Teleostome fishes shows the following features. 
In the Teleostei (Allis 1909a; Sagemehl 1885; 1891; Ridewood 1904a; 1904b; etc.) 
the cranial cavity is in the interorbital wall somewhat displaced to the dorsal side as 
is usual in Actinopterygians, and the ventral part of the interorbital wall is thin. The 
cranial cavity is often reduced also in the anterior part of the interorbital wall, and 
this part is then also thin and continuous with the thin ventral part. Under such circum¬ 
stances the anterior and basal parts of the interorbital was are thus reduced to a more 
or less thin interorbital septum. A fenestra optica is always present. The myodome is 
a rule well developed. The portion of the basis cranii, situated between the fossa hypo¬ 
physeos and the fenestra optica, is veryjthin and always considerably shortened. 
The ossifications present in the orbito-temporal region of the Teleostei are, as we 
know, a paired alisphenoid, a paired or unpaired orbitosphenoid and an unpaired so- 
called basisphenoid. The anterior part of the prootic also undoubtedly falls within this 
region. Of these bones the orbitosphenoid is very inconstant. The so-called basisphenoid, 
22* 
