1242 DR. ERIK A. STENSIO ; NOTES 



labyrinth region that is preserved are occupied by an unpaired 

 large bone, the sphenoid (Stensio, 1921, p. 56), while in the 

 ethmoidal region there is found a paired bone, the exethmoideo- 

 preethmoid (c.f. Stensio, 1922 «, pp. 184-185). Both the sphenoid 

 and the exethmoideo-preethmoid consist chiefly of cancellous 

 bone, and exhibit no centres of ossification nor any radiate 

 structure. 



"We begin our detailed descr;ption with the sphenoid. This 

 bone {S-ph, text-fig. 1 ; PI. I. figs. 1-4) is high at the posterior 

 end, but becomes rapidly lower forward, so that its height at the 

 anterior end is only about a third of that at the posterior one. 



Text-figure 1. 



c.ophHi.loS , 

 olsph ' _!_ 



,op^l^h.llli 



Dictyonosteus arciicus Stensio. 

 Anterior half of the neurocranium in lateral view. The lateral part of the ethmoidal 

 region removed, as are also the lateral parts of the dermal bones of the cranial 

 roof. Cartilage dotted. Somewhat more than a third of the natural size. 



E.pethm, exethmoideo-preethmoid ; Fr, frontal ; JPspJi, parasphenoid ; Sph, 

 sphenoid; a.car.int, canal for the arteria carotis interna; alspli, alisphenoid wulst ; 

 hp, hasipterygoid process ; en, orhito-nasal canal for vessels to or from or both to 

 and from the nasal fossa ; c.ophth.lat, canal through the alisphenoid wulst for the 

 n. ophthalmicus lateralis ; sj, sulcus for the vena jugularis (dorsal end of the sulcus 

 onlj' seen here) ; v.cerebr.ant, canal for the vena cerebralis anterior ; I, olfactory 

 canal ; II, opticus canal ; III, oculomotorius canal ; IV, trochlearis canal ; V, tri- 

 geminus exit ; Vi, canal for the r. ophthalmicus profundus ; VII, the probable 

 place of the facialis exit. 



The width of the bone taken as a whole is rather small, except 

 at the postero-ventral part where the basipterygoid process (bp) 

 is situated. The posterior end of the bone seems to have been 

 separated from the ossification, or the ossification following next 

 behind in the labyrinth region, by a synchondrosis, and that this 

 also has been the case anteriorly towards the exethmoideo- 

 preethmoid is certain. The former end is in side view angulated 

 in the way shown by text-fig. 1, the latter, on the other hand, 

 convexly arched. The cranial cavity extends forward through 

 the whole length of the bone. 



