78 
ERIK A : SON STENSIO 
1909a, pp. i 83 —208; 1914a, pp. 225— 253; 1918a, pp. 241—246). For it is evident that the 
musculus rectus externus must have extended throughout the entire ventro-medial half 
of the cavity to reach its supposed place of origin in the fossa my. Since, as far as 
can be judged, the other three musculi recti of the eye may have originated principally 
on the lateral surface of the basal region (bspli) of the sphenoid and the dorsal surface 
of the basipterygoid process, the posterior ends of these too have extend into the 
cavity and been situated in this medially and presumably also somewhat ventrally of 
the m. rectus externus. Further, n. oculomotorius and n. abducens had their exit in the 
same half of the cavity, the former nerve far forward, the latter far backward. Finally 
it is very probable (cf. Saurichthys ornatus part II) that v. jugularis in its backward 
course also entered this half, where, however, it would have turned fairly soon in a 
dorsal direction reaching the dorso-lateral half of the cavity. 
At the posterior part of this dorso-lateral half of the cavity the trigeminus and 
lateralis roots have pierced the medial wall of the cavity, which was rather thick at 
this place. A part of the ganglionic complex that was formed by these roots must 
presumably have been situated in the medial wall (incisure V in my figures), another 
part, on the contrary, probably had its position laterally of this in the cavity itself. 
Of the branches sent out from the ganglionic complex at least r. maxillaris, r. mandi- 
bularis and n. buccalis lateralis have had an anterior course through the dorso-lateral 
half of the cavity throughout its length. R. ophthalmus profundus or (a somewhat corres¬ 
ponding nerve) has had its exit far forward rather in the dorso-lateral than in the ventro¬ 
medial half or at the boundary between the two. Whether, finally, the roots for n. facialis 
closely accompanied the trigeminus roots and thus entered the most posterior end of 
the cavity or whether they pierced the cranial wall behind the cavity, must still be 
considered an open question. The trigeminus incisure (V, text figs. 62, 63 ; PI. 20, fig. 6; 
PI. 21, figs. 1— 3 ; PI. 22, figs. 1, 3 ) on the posterior margin of the sphenoid certainly 
seems by its size to indicate that the trigeminus and facialis roots might have had their 
exit together or in close proximity, but there is no real proof of this. 
As far as one can judge there has been at least no osseous or cartilaginous septum 
between the dorso-lateral and ventro-medial halves of the postorbital cavity, for on the 
lateral surface of the sphenoid there is no trace of a fastening for a septum of this 
sort. Whether, on the other hand, a membranous septum was present or not is very 
difficult to decide, except just at the very opening to the orbit. For at this opening 
we find on the medial side of the parasphenoid quite close to the lateral edge of the 
basipterygoid process a small dorso-medially directed process pd (text fig. 64 B) with 
about the same position as the ventral end of the process in Amia that Allis (1897 a, 
pp. 492—497; 1909a, pp. 3 g —41, 48; 1914a, pp. 246 — 248; 1918a, 244—245) called the 
alisphenoid pedicle. In Amia this process has its ventral end in contact partly with 
the cartilage laterally of the orbital opening of the myodome, partly with the processus 
ascendens of the parasphenoid. In the Teleostei Allis (1909 a, pp. 3 g —41, 45) has shown 
that a correspondence to the alisphenoid pedicle is present, although it is often represented 
only by a ligament issuing from a process or a ridge-like swelling of the alisphenoid and 
extending to the processus ascendens of the parasphenoid. The ligament may be partly 
or entirely ossified by «invading growths* from the alisphenoid and the parasphenoid. 
