1904.] OSTEOLOGY OF THE ELOPID^ AXD ALBULID.-E, 57 



this will apply even in cases where the combined bone has sunk 

 inwards and no longer presents itself as a supei'ficial bone of the 

 skull ; as, for instance, the prefrontals and postfrontals of Arapaima 

 and Osteoglossicm, in which genera so many of the dermal bones 

 are still dei'mal in position. 



Even if in these latter cases it be proved by histological investi- 

 gation that the bone is a pure cartilage-bone, the argument is not 

 the less sound. The ossification in the cartilage owed its origin 

 phylogenetically to a predisposing dermal ossification which 

 now no longer appears in ontogeny. The terms parethmoid, 

 sphenotic, and pterotic are, therefore, redundant ; and if the 

 occasion arises for discriminating the two parts of the prefrontal, 

 postfrontal, and squamosal, they should be distinguished by the 

 terms ectosteal and endosteal. This practice has hitherto been 

 followed, more or less, in the case of the articular and palatine 

 bones. The two constituents of the palatine of Amia, for instance, 

 are called exosteal and endosteal by Bridge (Journ. Anat. and 

 Phys. xi. 4, 1877, p. 616), while Allis (Journ. Morph. xii. 3, 1897) 

 alludes to them as the dermopalatine and autopalatine, employing 

 the prefixes introduced by van Wijhe (Nied. Arch. f. Zool. v. S, 

 1882). The question of ectosteal and endosteal ossification^ in 

 fishes has already been discussed at some length by Yrolik (Nied. 

 Arch. f. Zool. i. 3, 1873), Gegenbaur (Morph. Jahrb. iv. Suppl. 

 1878), Pouchet (Journ. Anat. et Phys. xiv. 1878), van Wijhe 

 {I. c. 1882, p. 210 et seq.), and McMurrich (Proc. Can. Inst. ii. 

 3, 1884, p. 280 et seq.) ; and Scl^mid-Monnard (Zeitschr. f. wiss. 

 Zool. xxxix. 1883) has recorded some valuable observations on the 

 mode of origin of such bones as the epiotic and squamosal in 

 Teleostean fishes. 



More recently, Swinnerton (Quart. Journ. Micro. Sci. 1902, 

 p. 531, footnote) has suggested the prefixes dermo-_ and chondro-, 

 " the former being used for bones which are quite free of ^ the 

 cartilage, and the latter for those which involve ci-»rtilage,_ irre- 

 spective of the degree of ossification in this, or of the retention of 

 dermal characters." This does not seem, however, to be a very 

 satisfactory solution of the difficulty. 



Cranial Bones. — The meeting of the two parietal bones in the 

 median line is, upon palaeontological grounds, a more primitive 

 condition than the separation of these bones by the supraoccipital, 

 no separation of the parietals occurring in pre- Cretaceous Isospon- 

 dylous fishes (Smith Woodward, Yert. Palaeontology, 1898, p. 113). 

 We have thus, to all appearances, one sound character by which 

 to test the relative tendency towards specialisation among Teleo- 

 stean fishes. But the possibility of a secondary approximation of 



superficial to the pterotic and iuieparable frora it, do not treat the terms postfrontal 

 and sphenotic in the same wa^', on the ground that the term postfrontal " cannot be 

 correctly applied to a membrane-bone in Fishes." Why it cannot, they do not 

 explain. , 



