6 4 
ERIK A : SON STENSIO 
of the bone substance was not particularly great, is given in text fig. 21b. The bone 
is pierced throughout its length by a sensory canal and has the centre of ossification 
situated in the posterior half, rather near the posterior end. 
The presence of a dorso-medial surface on the supratemporo-extrascapular bone, 
taken in connection with the shape of the bone otherwise, speaks strongly in favour, 
it seems to me, of a paired muscle fossa (fossa temporalis, Allis, 1897 a, PI. XXI, fig. 8; 
1909 a, pp. 8—12) having been developed on the posterior part of the labyrinth region. 
Text fig. 21 a shows how one can imagine such a muscle fossa (f. temp.) would appear. 
Of course this figure can make no claim to be accepted as fully correct, as one has 
no point from which to judge of the extension of the fossa either forwards or medially. 
It it also clear from the same figure that the dorsal surface of the primordial neuro¬ 
cranium in this region was not directly covered by the dermal bones, but that these 
bones — the extrascapular bones — were situated loosely in the skin above the 
muscles, which reached into the two fossae described to take their insertion in them. 
Nothing is, however, preserved of the extrascapular bones referred to here. 
In the labyrinth region too, but on its side wall, one finds certain hints of the 
presence of another fossa, which certainly must have been shallow, but in other respects 
of considerably larger dimensions than the dorsal one just described. This lateral fossa has 
been bounded dorsally by that part of the parieto-intertemporal bone which lies laterally 
of the line along which the perpendicular longitudinal lamella issues, and further by the 
most anterior part of the supratemporo-extrascapular bone; posteriorly by the process li 
and also by the posterior part of the corpus of the prootico-opisthotic. Its ventral 
and anterior boundaries are, on the contrary, very vague. In connection with my de¬ 
scription of the visceral skeleton below, I shall return to this fossa and what it may mean. 
As we have seen, in the part now dealt with of the dermal roof of the cranium 
in W. sinuosa and other Coelacanthids the number of bones is limited to two on each 
side of the median line, if one excepts the bones of the extrascapular (supratemporal) 
row. The Rhipidistidia are in this respect more primitive, as the investigations of Traquair 
('1875 a, 1881, 1896), Watson and Day (1916), and also Goodrich (1919) have proved. The 
number of membrane bones in the corresponding part of the cranial roof of these fishes 
is, as a rule, three on each side median line, which have been called by Watson, Day 
and Goodrich the parietal, the intertemporal and the supratemporal respectively. Of these 
the intertemporal has such an extension and is pierced by a sensory canal in such a way 
that its homologue in the Coelacanthids cannot be an independent bone (cf. the descrip¬ 
tion of Axelia robusta below) but may be fused with the parietal and in consequence 
the term parieto-intertemporal bone, as I have proposed, must be quite justified. 
The supra-temporal of the Rhipidistidia corresponds to the anterior part only of 
the supratemporo-extrascapular bone of the Coelacanthids. The posterior part of the 
supratemporo-extrascapular of Coelacanthids belongs, as ought already to be under¬ 
stood from the name, to the extra-scapular series, and has its nearest homologue, as- 
I can show below in the description of a species belonging to the genus Axelia, in the 
lateral extrascapular bone of the Actinopterygians, or in a lateral part of that bone 
in the Rhipidistids, which Watson and Day, and after them Goodrich, have called the 
tabular bone. 
