94 
ERIK A : SON STENSIO 
modify its form in any way. The bone in question is only half as high as the part of 
the region in which it is situated. It is shaped almost like a three-sided prism with a 
ventral horizontal surface, a lateral one that is vertical, and a dorso-medial one that 
has been attached to the cartilage. The posterior and anterior ends have also been 
joined to cartilage, as text fig. 3 9 shows. The bone is considerably broad and it is open 
to question whether it has not met that of the opposite side in a median suture. The lateral 
side has throughout its length, close to the ventral margin, a distinct, rather broad 
and deep groove (ms, text figs. 3 g, 42; Pis. 12, 1 3 ; PI. 16, fig. 1), which towards the 
anterior end of the bone, leads into a canal (lat. for) which in its turn continues in 
an antero-medial direction. 
The ventral side has in its anterior part towards the medial margin a small 
foramen (f. pal, text fig. 42; Pis. 12, 1 3 ; PI. 16, Eg. 1) which leads into a fine, verti¬ 
cally ascending, canal. The ventral side of the bone is in its median parts covered 
by the parasphenoid as shown in text fig. 42, and PI. 16, fig. 1. The relation between 
the bone and the cartilaginous parts of the ethmoidal region is easy to understand 
from text fig. 3 g. It may, however, be specially emphazised that it by no means reaches 
backwards to the orbit. 
It thus seems probable that this bone bears a close resemblance to the preethmoid in 
Amia, although it is considerably more powerfully developed than in this form (Sagemehl x 884, 
p.204; Allis 1897 a, PL XXI, figs. 8—10; 1898, pp. 446—450: 1909a, pp. 17—22; Swinnerton 
1902, pp. 530— 53 1). In the groove on the lateral side branches of ramus maxillaris 
superior trigemini and buccalis lateralis have apparently had their course, the latter for 
the innervation of the most anterior sensory organs of the infraorbital canal. The fine 
vertical canal ascending from the ventral side seems to have a dorsal branch of the 
nervus palatinus anterior running through it. In Amia this nerve does not penetrate 
the preethmoid but is situated close to its medial margin. Thus it might easily be en¬ 
closed in this bone if there were a medial growth of this(cf. Allis 1897 a, PI. XXI, figs. 8,10). 
The membrane bones of the neurocranium. 
The parasphenoid Psph, text fig. 3 g, 40, 41, 42; PI. i 3 ; PI. 14, fig. 5: PI. 16, fig. 1) 
has the same extension as in W. sinuosa, i. e. it covers the whole basal surface of 
the orbitotemporal region and also stretches anteriorly under the ethmoidal region and 
posteriorly, although only to a slight extent, under the most anterior part of the labyrinth 
region. Its anterior end does not reach forward under the ethmoidal region quite so 
far as to the anterior end of the preethmoid (text figs. 3 g, 42, PI. 16, fig. 1), and it 
covers only the posterior medial part of the latter bone (cf. W. sinuosa text fig. 23 ). It 
is much thicker and stouter than in W. sinuosa and is also of a different shape. Its 
most distinguishing feature is, on the whole, its great breadth. The anterior end forms 
an obtuse angle, the posterior end is truncated and slightly concave.. The greatest 
breadth lies near the anterior end and behind that comes a somewhat narrower part, 
while about and just behind the middle it becomes broader again, but not so broad as 
in the anterior part, after which it gradually grows narrower towards the posterior 
end, immediately in front of which lies the narrowest part. The centre of ossification is 
so situated that it corresponds to the posterior of the two broadest parts. 
