TRIASSIC FISHES FROM SPITZBERGEN 
I&5 
part of the «prootic'al bridge* in Amia and Teieosts (cf. Allis, 1897, a, pp. 492—497; 
PL XXI, fig. 11; 1909 a, pp. i 83 — 2o3). Nor does it seem impossible that the anterior part 
of the region pc should also have a corresponding part in Lepidosteus in the roof 
of the transversally situated cavity that is considered by Sagemehl (1885, p. 86) to 
be homologous with the canalis transversus of the Elasmobranchs (cf. Allis, 1909 a, 
pp. 188—189). With regard to this it is noteworthy that the roof of the cavum sacci 
vasculosi consists in Polypterus of a bone lamella belonging to the sphenoid as in 
B. mougeoti, while the «prootic bridge« in Amia and Teieosts and its equivalent, the 
roof of the mentioned transversal cavity, in Lepidosteus, are formed by a medial process 
from the prootic of each side. 
While the cavum sacci vasculosi in Polypterus is, as we know, fairly large and 
has a rather great extension in the rostro-caudal direction and communicates with the 
cranial cavity by means of a wide opening, the fossa hypophyseos in B. mougeoti forms 
a fairly narrow, vertical pit in the floor of the cranial cavity and it is only this pit that, 
as we have seen, is, by means of a foramen in its floor, in communication with the 
transversal canal in the basis cranii. 
In Lepidosteus the transversal cavity in the basis cranii is, as we know, closed at 
both ends, and the vena pituitaria (sinus transversus) pierces the cranial base rostrally 
of it (Allis 1909a, pp. i 83 —190; 1914a, pp. 241—243; Veit 1907, p. 199; Sagemehl 1885, 
p. 86). In Polypterus, on the other hand, we find the wall of the «cavum sacci vasculosi» 
pierced on each side by a foramen that obviously transmits v. pituitaria (Lehn 1918, 
p. 364 ), and this vein seems to occupy a somewhat corresponding position in relation 
to the fossa hypophyseos in fishes in general (Allis 1909a, pp. i 83 —208; 1911, p. 291; 
1914a, pp. 225—253; 1914b, p. 627; Allen 1905, p. 81, PL II, fig. 15; Greil igi 3 , p. 1260; 
O’Donoghue 1914, pp. 440—441). It is noteworthy that in Elasmobranchs it has been 
found to pierce the transversally running canal in the basis cranii for which Gegenbaur 
(1872, pp. 75—79) introduced the term canalis transversus. 1 ) 
If we now examine the conditions in the pars basalis of the sphenoid in B. mougeoti 
with reference to the course of v. pituitaria it is clear that this vein must have pierced 
the transversal canal (c. transv.) beneath the anterior end of the region pc. The trans¬ 
versal canal itself must certainly be homologized with the canalis transversus of the 
Elasmobranchs, and I shall accordingly refer to it by this term in the sequel. It is 
difficult to decide with certainty whether it was bridged over ventrally by the para- 
sphenoid alone or whether its ventral boundary besides consisted to some extent of 
cartilage. It seems, however, beyond all doubt that at any rate there was a larger or 
smaller gap, probably corresponding to a fenestra basicranialis anterior, ventrally of 
the canalis transversus. 
If my view referred to above of the position of the infundibulum and the hypo¬ 
physis of B. mougeoti is correct, the mesencephalon and the anterior part of the medulla 
oblongata must have been situated above the region pc of the pars basalis of the 
sphenoid. The foramen (fen. bas. post, text fig. 63 B, C; Pl. 21, fig. 1, 2; PL 22, fig. 3 ) 
which, as has been mentioned, pierces this region, can clearly not be placed in any 
q Allis (1914a,b;) lias tried later on to establish the name «pituitary canals for this canal on account of 
its relations to v. pituitaria. 
