ERIK A : SON STENSIO 
which is bridged over by the parasphenoid ventrally so that a transversal canal arises. 
The diameter of this canal had, as is shown by text fig. 63 C, its greatest height immediately 
behind the region bsph, from which it follows that this region becomes very sharply 
cut of from the one following behind it. 
Along the ventro-lateral margin of the region bsph there issues a paired, large but rather 
thin process (bp, text figs. 63 A, B, 64 B; PI. 22, fig. 1, 2). The process extends in caudal 
direction past the transversal canal (c. transv.) in the basis cranii, forming the ventral 
boundary for the exit of this canal. Because of the development of the processes bp 
the posterior margin of the region bsph appears in ventral aspect very concave, while 
the anterior margin, in the same aspect, appears convex (text fig. 63 B; PI. 21, fig. 1). 
A median sagittal section through the sphenoid (text fig. 63 C) shows that the 
region bsph dorsally of the fenestra optica is closely attached to the regions of the pars 
basalis situated in front of it. As a similar section also shows, the floor of the cranial 
cavity has its highest point in the orbitotemporal region situated about over the posterior 
end of the fenestra optica and from this sinks more slowly forwards than backwards. 
Immediately behind the region bsph there follows on the dorsal surface of the 
pars basalis of the sphenoid, i. e. on the floor of the cranial cavity, a deep and rather 
narrow fossa (/. hyp, text fig. 63 C; PL 21, fig. 2), which pierces the basis cranii and 
opens into the above described transversal canal (text fig. 63 B,C; PI. 21, fig. 1; PI. 22, 
fig. 3 ). Posteriorly this fossa is bounded by a fairly thin bony part (dors, sell, text 
fig. 63 C), which forms the most anterior end of the region pc. From this place this 
region sinks backwards until its ventral surface is at about the same level as the 
ventral surface of the region bsph and this sinking also affects the basal surface of 
the cranial cavity, which as a matter of fact is also hollowed out in the longitudinal 
direction of the cranium so that its median parts are situated more deeply than its 
lateral ones. With regard to the region pc of the pars basalis of the sphenoid it is 
noteworthy in this connection too that it is pierced by a large oval foramen (fen. bas. 
post, text fig. 63 B, C; PI. 21, figs. 1, 2; PI. 22; fig. 3 ), and that in its posterior part it 
is sharply cut off from the partes laterales of the same bone (here the processes c ) 
by a paired, narrow but deep incisur (fi) penetrating from the back. 
The fossa described above (f. hyp), which opens into the transversal canal, undoubtedly 
represents the fossa hypophyseos and the region of the pars basalis of the sphenoid 
situated in front has, as far as can be judged, a partial correspondence in Amia in the 
cartilage lying between the hypophysis and the fenestra optica, called the transversal 
«Wulst» (Allis, 1897 a, p. 493; PI. XXI, figs. 9, 11, w) and in Teleosts in their so called 
basisphenoid. At least the upper and the middle parts of the fossa have certainly been 
occupied by the infundibulum. The hypophysis would therefore have been situated in 
its ventral parts and probably extended also down into the basal transversal canal. It 
seems very probable that the saccus vasculosus too was situated with it in this canal. 
Under these circumstances it is clear that the anterior part of the region pc in the pars 
basalis of the sphenoid would correspond both in function and position to the roof of 
«cavum sacci vasculosis in Polypterus l ) (cf. Lehn, 1918, p. 36 ^, fig. 4), and to the anterior 
J ) The name cavum sacci vasculosi for the space in question in Polypterus is incorrect, as both the hypo¬ 
physis and the saccus vasculosus are situated in it (cf. Lehn 1918, p. 064, figs. 9—12; Tafel.XVII), 
