TRIASSIC FISHES FROM SPITZBERGEN 
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the labyrinth region forms the widest part of the neurocranium. In Birgeria it grows 
rapidly narrower in its posterior part and in this way passed over into the occipital 
region, of whose shape and extension nothing is known. 
In the primordial neurocranium ossifications are generally found developed (Traquair, 
1877a, p. 16; Fritsch, 1895, p. 123 ), but details as to these are only known in Birgeria 
and Acrorhabdus. 
In both these genera the ossifications, at least in the orbitotemporal and labyrinth 
region, are considerable and the cartilaginous parts in these regions were therefore 
relatively small. The ossifications are strong and thick, consisting of cancelleous bone 
substance throughout. No traces of ossificatory centres can be found, nor radiation 
either. Their periostal lamellae are very weak and thin. 
In the occipital region a basioccipital is developed which with its anterior end 
extended into the posterior part of the labyrinth region. If any other occipital bones 
were present is not known. The chorda may have extended through the whole occipital 
region and may also have continued a good bit into the labyrinth region. 
In the labyrinth, region there are two paired ossifications, the autosphenotic and the 
prootico-opisthotic, the latter of which probably corresponding not only to the components 
indicated by its name 1 ) but to the epiotic as well. 
The autosphenotic is a somewhat elongated bone in the postorbital process. 
The prootico-opisthotic occupies a considerable part of the lateral wall of the 
labyrinth region. It extends forward to the canalis facialis, backwards presumably right 
to the boundary towards the occipital region. Its dorsal parts extend medially into the 
tectum synoticum, where farthest back they are even so developed that they meet the 
corresponding ones of the bone on the opposite side in the median line. Otherwise the 
bone surrounds more or less directly the greater part of the labyrinth and is presumably 
pierced by n. glossopharyngeus. 
The most anterior part of the labyrinth region in front of the prootico-opisthotic 
has been cartilaginous in the roof, lateral walls and floor, and through this cartilage the 
roots of n. facialis have their exit from the cranial cavity. From the ganglionic complex 
of these roots the truncus hyoideomandibularis was given off and took its course for a 
short distance postero-laterally through the rather wide facialis canal, through whose 
posterior opening it definitely left the cranial wall. The roots of n. trigeminus, n. ophthal¬ 
micus lateralis and n. buccalis lateralis left the cranial cavity just in front of the facialis 
roots, at the posterior margin of the large unpaired ossification that occupies practically 
the whole orbitotemporal region. A trigemino-facialis chamber has probably been present, 
but it is uncertain whether the ganglionic complex of the facialis roots was situated in 
this together with that of the trigeminus roots. 
The large unpaired ossification mentioned in the orbitotemporal region has been called 
by me the sphenoid according to the terminology of Traquair 1871, in his description 
of Polypterus. Forward it reaches quite or at least almost to the ethmoidal region and 
backward right to the cartilage in the anterior part of the labyrinth region. Basally a 
s ) It is very noteworthy that in the Coelacanthids too a large paired prootico-opisthotic is present in the 
labyrinth region. This prootico-opisthotic, however, does not include any epiotic component. Is would of course be 
of great theoretical interest to know the conditions of Dictyonosteus in this respect. 
