1248 DR. ERIK A. STENSIO : NOTES 



situated on the ventral surface of the region, the former of 

 which represents the external, and the latter the internal, nasal 

 aperture. In the present state of preservation, dermal bones 

 form the direct boundary of the external nasal aperture on the 

 dorsal side and of the internal nasal aperture anteriorly, but it is 

 conceivable that in the fresh specimen these walls of the two 

 nasal apei'tures consisted, at least in part, of cartilage. 



The r. maxillaris trigemini and the n. lateralis buccalis ought 

 as usual to have had their course along the ventral edge of the 

 lateral surface of the ethmoidal region, but owing to the im- 

 perfect state of preservation of these parts of the region it has 

 not been possible to discover whether a distinct sulcus was 

 developed for them as in several other fishes (Stensio, 1921, 

 p. 94 ; 1922 h). For the same reason it has not been possible to 

 establish anything with regard to the ai-ticulation facet for the 

 anterior end of the palatoquadrate. 



From the facts put forward here it is easily seen that the 

 exethmoideo-preethmoid is so developed that it represents both 

 the exethmoid and preethmoid {cf. Stensio, 1921, pp. 93-94; 

 1922 «, pp. 184-186). 



Dermal Bones of the Primordial Neurocranium.. 



The parasphenoid {Psi^li, text-figs. 1, 2; PI. I. figs. 1, 2,4; 

 Stensio, 1918 5, pi. v. fig. 1) is imperfectly preserved at both 

 -ends. The preserved parts of it cover the whole ventral surface 

 of the sphenoid and the ventral surface of the exethmoideo- 

 preethmoids in the posterior two-thirds of their length. It thus 

 cannot have extended much farther forward, and it is also 

 conceivable that only a rather small part is lacking at its 

 posterior end. There is no processus ascendens. The centre 

 of ossification is clearly distinguishable, and situa.ted midway 

 between tlie posterior and anterior ends of the bone. At this 

 place and for some distance forward and behind it the bone is 

 much bi'oader than the ventral surface of the sphenoid, so that 

 it projects here with a free lateral part on either side of this 

 (text-fig. 2). 



Just at the centre of ossification a ra.ther fine median, unpaired 

 ca.nal opens on the venti-al surface of the parasphenoid. The 

 canal perforates the parasphenoid obliquely upwards and back- 

 wards, then continuing backwards between this and the ventral 

 surface of primordial neurocranium towards a. place between 

 the ventral openings of the internal carotid canals. The 

 canal ought, so far as one can judge from the conditions in 

 Amia (Allis, 1897, pp. 620-621 ; pi. xxxvi. fig. 61; pi. xxxvii. 

 figs. 62, 63), to ha.ve been traversed by the anterior branches of 

 the rami palatini of the facialis nerves, which ought to have 

 accompanied the internal carotid arteiies when these entered 

 between the sphenoid and the ventral surface of the primordial 

 iieurocranimn. Possibly the canal in question for the anterior 



