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ERIK A : SON STENSIO 
that it seems to meet that of the opposite side in the median line or at any rate to 
come very near this. Otherwise the ethmoidal. region was cartilaginous throughout, both 
anteriorly, posteriorly and dorsally of the preethmoids. 
In the posterior part of the orbitotemporal region and the anterior part of the 
labyrinth region, i. e. above the basisphenoid corpus, the cranial cavity is situated very 
high above the basis cranii. In front of the basisphenoid corpus it sinks rapidly, forming 
a deep and long fossa hypophyseos, and even at the back, towards the occipital region, 
it seems to have sunk down, though more slowly. Thus behind the fossa hypophyseos 
one has a large dorsum sellae, formed by the basisphenoid corpus. In an anterior direction 
the cranial cavity has probably, as in Dictyonosteus , extended through the whole orbito¬ 
temporal region. 
It is impossible at present to localize exactly the place of exit of the vagus nerve 
and this is also the case to a certain extent with the n. glossopharyngeus, although this 
cannot, however, in any case have had its exit far behind the corpus of the prootico- 
opisthotic. Finally the relations of the n. acusticus to the cranial wall are also rather 
uncertain. On the other hand n. facialis seems to have penetrated the cranial wall between 
the basisphenoid corpus aud the dorsal process of the prootico-opisthotic. Of the trigeminal 
branches probably r. maxillaris, r. mandibularis and with them r. ophthalmicus superficialis 
have emerged through a foramen above the basisphenoid corpus immediately behind the 
basipterygoid process. Either together with these or immediately dorsally of them 
n. ophthalmicus lateralis has left the cranial cavity and in certain forms, e. g. Axelia, 
the course of this nerve can be clearly traced in a fine horizontal sulcus across the 
lateral surface of the alisphenoid (the ventro-caudal process from the fronto-dermosphenotic). 
R. ophthalmicus profundus or a partly corresponding nerve may have issued in the 
orbit in front of the basipterygoid process through the upper part of the forward 
pointing lamella of the basisphenoid. The places of exit for n. trochlearis, n. oculomotorius 
and n. opticus have, as far as can be understood, been situated in the cartilaginous 
part of the interorbital wall. Nothing certain is known with regard to n. abducens. It 
is conceivable that this nerve had its exit together with r. maxillaris and mandibularis 
trigemini, which may sometimes be the case in a number of recent fishes. 
The nasal capsule was situated above the posterior part of the preethmoid and 
opened outwards with two foramina situated close together, an anterior and a posterior 
one. The preethmoid has on its lateral side at the base a distinct longitudinal furrow, 
which continues anteriorly in a somewhat medially and upward directed canal. The 
furrow and the canal have certainly been related to the anterior branches of the 
n. buccalis lateralis and the r. maxillaris trigemini, both of which, as is usual in fishes, 
continued along to the most anterior part of the nose. The preethmoid is penetrated 
from the ventral side by a dorsally ascending fine canal, probably for a branch of 
r. palatinus anterior. 
The eye-bulbs were large, as already mentioned, and a bony sclerotic ring is 
always developed. 
The membrane bones of the neurocranium. The parasphenoid is large and 
in the majority of Carboniferous Permian and Triassic forms it is wide, while in a large 
number of Jurassic forms and at least in Macropoma among the Cretaceous ones it is 
