1244 DR. ERIK A. STENSIO : NOTES 



latter surface suddenly deepens to a postero-ventrally directed 

 fossa hypophyseos, which extends nearly to the postero-ventral 

 corner of the pars basalis {f.hyp, PI. I. fig. 2), where it is 

 separated from the synchondrosis behind the sphenoid only by a 

 very thin layer of bone. So far as is known, the fossa hypo- 

 physeos does not in any way open on the base of the primordial 

 neurocranium or in the mouth. 



On either la.teral surface of the pars basalis there is found, as 

 already mentioned, farthest posteriorly the lai-ge basi pterygoid 

 process {hp). This process partly arises along the ventral, partly 

 along the posterior edge of the lateial surface, and extends rather 

 high upwards, ending doi'sally with a truncated end. The 

 process has a dorsal surface represented by a truncated dorsal 

 end, a postero-ventral surface which has been attached to carti- 

 lage, a ventro-lateral surface against which the metapteiygoid 

 probably articulated, aud an antero-dorsal surface which, together 

 with the lateral surface of the pa,rs basalis just anterior to it, 

 forms a rather shallow and indistinct fossa directed with its 

 opening antero-laterally and somewhat dorsally. 



In this fossa there opens a wide canal, which perforates the 

 pars basalis in a transverse direction below the fossa hypo- 

 physeos to the corresponding fossa on the opposite side. This 

 canal (v.pit, PI. I. figs. 2, 4) communicates with the fossa hypo- 

 physeos by a short but wide posteriorly directed branch, and, 

 though it runs ventrally of the posterior part of the fossa 

 hypophyseos, must undoubtedly be the canalis transversus, and 

 have been pierced by the pituitary vein (AUis, 1914; 1919 a; 

 cf. also Stensio, 1922 a). From its external opening in the fossa 

 described there a very distinct sulcus (sj, text-fig. 1 ; PI. I. fig. 4) 

 leads upwards to the dorsal end of the basipterygoid process, a 

 sulciis which must have been developed for the jugular vein 

 (c/. AUis, 1919 «; Stensio, 1922 6, loc. cit.). Accordingly there 

 is no doubt that this vein in its continuation backwards must 

 have run dorsally of the basiptei-ygoid process. 



Immediately in front of the basipterygoid process of either 

 side there is found close to the ventral edge of the lateral surface 

 of the pars basalis a large oval foramen (a.car.int, text-fig. 1 ; 

 PI. I. figs. 1, 2, 7) apparently leading into a vertical canal 

 ascending to the cranial cavity. This canal, which must be the 

 canal for the arteria carotis interna, ought to have entered the 

 cranial cavity not far anterior of the fossa hypophyseos, between 

 this and the opticus exit, and thus quite in the normal way 

 {cf. Allis, 1897; 1909; 1911a., b; 1912 «, h; 1914; 1919 a; 

 Allen, 1905; Danforth, 1912; Stensio, 1922 &). 



The partes laterales of the sphenoid (text-figs. 1, 2; PI. I. 

 figs. 1-4) do not diverge much from one another upwards, thus 

 occupying an almost vertical position. Anteriorly they are 

 rather thin, but they grow slowly thicker backwards. Along 

 their dorsal margins, too, they are partly thin, and so developed 

 as to show that the roof of the primordial neurocranium in the 



