SKULL 



227 



le 



confluent with their respective epiotics. The floor and side walls 

 of the inter-orbital section of the cranium are formed by a remark- 

 able " sphenethmoid " bone which occupies the position of the 

 paired ali- and orbito-sphenoids in other bony Fishes ; and in one 

 species, P. lapradei, 1 it forms in front distinct tubular investments 

 round the olfactory nerves. In many respects this bone is singu- 



FiG. 132. A, side view 

 of the skull of PO/I/JI- 

 terits ; B, dorsal view, 

 showing the chief 

 dermal boues : C, 

 similar view of the 

 chondro-cranium after 

 the removal of the 

 dermal bones. An, 

 Angular ; Ar, articu- 

 lar ; Z), dentary ; E, 

 mesethmoid ; f.m, 

 foramen magnum ; 

 Fr, frontal ; l.e, lateral 

 ethmoid ; MX, max- 

 illa ; Xa, JVrt', nasal 

 and accessory nasal 

 bones ; occ, occipital ; 

 ol, nasal aperture ; 

 Op, operculum : "//.. 

 opisthotic ; O.t, os 

 terminale ; Pa, pari- 

 etal ; Pm.z: pre- 

 maxilla ; P.t, post- 

 temporal ; Ptf, J.dsl- 

 1'rontal ; Qu, quad- 

 rate ; .S'A W, cir- 

 i- 11 in -orbital ossicles : 

 *.<>p, sub-operculuni ; 

 Sp, splenial ; .//. (//', 

 spheuethmoid ; sp.o, 

 sphenotic ; ^i"", 



spiracular ossicles, between which is the spiracle ; S.t, supra-temporals ; Y, cheek-plate 

 (pre-operculum) ; I", Y", smaller cheek-plates ; z, z, 2, ~, post -spiracular ossicles ; 

 2', 2', prespiracular ossicles. In C the cartilage is dotted. (From Traquair.) 



larly like the sphenethmoid bone of the Frog and other tailless 

 Amphibia. A median ethmoid as well as lateral ethmoids are 

 present. In addition to the ordinary dermal bones which invest 

 the cranial roof there is a transverse row of supra-temporal 

 plates crossing the cranial roof behind the paired park-la Is 

 (Fig. 132, A). Fringing the outer margins of the frontals 

 and parietals a row of pre- and post-spiracular ossicles extends 

 nearly to the orbits, and between two of them, which form a 



1 Budgett, Trans. Zool. Soc. xv. 1900, p. 334. 



