ON CERTAIN CaOSSOPXERYGIANS. 1253 



extends, contrary to that in Dictyonosieus, far forward in the 

 ethmoidal region, thus probably including in its anterior parts 

 the homologues of the exethnioideo-preethmoids (c/". pp. 9-10 

 above). Bryant's account of the anterior parts of the bone 

 is, however, very incomplete, and as in addition the figures 

 he publishes are not very distinct and kick letters of I'eference, 

 it is impossible to understand how the conditions actual!}'- are 

 there. 



In accordance with the conditions in LiciyonQsteus and 

 Di'plocercides the n. trigeminus must have pierced the carti- 

 laginous part of the cranial wall just behind the dorsal half of 

 the sphenoid. The exit of the n. facialis has probably been 

 situated somewhat more postero-ventiully, though also in the 

 cartilaginous part of the cranial Vs'all behind the sphenoid (rf. 

 Stensio", 1922 a). 



If my opinion, just given, with regard to the position of the 

 trigeminus and facialis is correct, it follows from this that the 

 small cartilage bone that is seen in Bryant's text-tig. 5 immediatelv 

 beneath the dermal cranial roof some distance behind the 

 sphenoid would be homologous with a dorsal part of the process 

 lettered /, by me in the post-Devonian Coolacanthids (Stensio, 

 1921), and the corresponding antero-dorsal part on either side of 

 the compound occipito-labyrinth ossification in Diplocercides. 

 This small cartilage bone is, however, so far as I can find, not 

 mentioned by Bryant in his description. 



The upper part of the alisphenoid wulst is pierced by a 

 horizontal canal for the n. ophthalmicus lateralis, exactl}^ as in 

 Dictyonosteus. The anterior opening of this canal is seen in 

 Brj^ant's text-fig. 5 and also, though less distinct, in his pi. ix. 

 fig. 3. The presence of this canal is undoubtedly a sti-ong 

 support for my view, given above, as to the position of the exit^ 

 of the n. trigeminus and the n. facialis. 



The canal which is stated by Bryant to open in a recess on the 

 external surface of the sphenoid just anterior of the basipterygoid 

 process, must evidently have transmitted the pituitary vein. 

 According to Bryant it leads forwards to a "chamber "on the 

 posterior basal part of the sphenoid — a " chamber " which is said 

 to be open behind and which, with some doubt, is taken to be the 

 anterior end of a myodome. That the "chamber," which in 

 another place is termed by him a " pocket," cannot be a part of 

 a myodome is evident, and it is quite certain that no posterior 

 myodome was developed, but tha,t the conditions were as in 

 Dictyonosteus in this respect. If the statements given by Bryant 

 were correct, the "chamber" in question would therefore be the 

 ventral part of the fossa hypophyseos. As, however, as far as can 

 be judged, it is very wide, I feel inclined to think that Brj-ant may 

 have made a similar mistake as I did in 1918 when describing the 

 corresponding part of the sphenoid in Dictyonoste%is {of. p. 1242 

 above). I thus rather fear that in the "chamber" we are 

 Peoc. Zool. Soc— 1922, No. LXXXIII. 83 



