OIs CERTAIN- CROSSOPTEEYGIANS. 1265 



traBsmittecl the n. ophthalmicus lateralis (c/*. also Stensio, 1921, 

 p. 170) and lower, a short distance above the dorsal end of the 

 basipterygoid process, the anterior opening of another canal, 

 which seems to have transmitted their r. ophthalmicus profundus 

 or some similar nerve.'" 



"The main part of the trigeminus nerve, together with the 

 lateralis nerves accompanying the trigeminus branches, has 

 traversed the cranial wall rather high postero-dorsally of the 

 basipterygoid process behind the alisphenoid wulst, and must 

 then have run forward and a little downward dorsally of this 

 process. Tlie facialis exit must have been situated still somewhat 

 farther backward, but at the same time cei'tainly also moi'e 

 ventrally than the trigeminus exit. The r. pah\tinus facialis 

 has been thence given off" in a forward and downward direction, 

 and it probably came down behind the basipterygoid process, 

 afterwards turning in a forward direction on the outside of the 

 basal part of this process. In this part of its course tlie r. pala- 

 tinus facialis ought to have been situated, at least for some 

 distance, rather close to the arteria. carotis interna. The 

 n. abducens probably accompanied the trigeminus branches, and 

 thus passed dorsally of the basipterygoid process. Finally, it 

 may also be pointed out that the large fossa hyphphyseos reaches 

 with its postero-ventral part into the part of the sphenoid 

 situated between the basipteiygoid processes." 



"From the facts stated, it is obvious that the formation in 

 Bictyonosteus tiiat has hitherto been called the basipterygoid 

 process must really in its antei-o-ventral part be homologous with 

 a posterior larger part of the basipterygoid process in Birgeria^ 

 at the same time, however, also including something more than 

 this. It would have about its entire correspondence in Birgeria 

 if we supposed there the myodome half of one side with the 

 exception of the prepituitaiy part to be filled out with bone and 

 this bone-mass forming a connected whole with the basipterygoid 

 process forward and downward, and also with the basal parts of 

 sphenoid on the medial side. In a similar way it would have 

 its equivalent in Amia if in this fish we supposed the lateral 

 parts of the myodome of either .side, apait from the prepituitary 

 part, to be filled with bone or cartilage, but in this case of 

 course it would correspond exactly only to the anterior part 

 of such a bone or cartilage mass. In sharks it corresponds some- 

 what but not quite exactly to a posterior part of what Allis 

 (1914 a) calls the ' subocular shelf — together with an adjoining- 

 part of the capsula auditiva postero-ventrally of the vena jugu- 

 laris. The correspondence would in the latter case be alnrost 

 complete if only these cartilaginous parts in the sharks were 

 developed somewha,t more in such a way as to form a lateral 

 wall, to some extent more complete, for the fossa at the posterior 

 end of the orbit in which the canalis transversus opens out. and 

 in which the trigeminus ganglionic complex is also usually 



