396 
CROSSOPTERYGII. 
other, covering the space behind the eye, and immediately below 
these is another ornamented membrane-bone, triangular in shape, 
elongated antero-posteriorly, and named post-maxillary by Huxley. 
A single narrow, arched, suborbital element extends from the post¬ 
orbitals to the edge of the anterior portion of the cranial roof ; and 
below this are indications of a long and narrow dentigerous maxilla, 
ornamented on its external aspect. The latter bone is termed pala¬ 
tine by von Zittel and Reis, but, as already perceived by Huxley, 
it has much more the appearance of an external element. The 
premaxilla is not certainly known. The greater portion of each 
mandibular ramus is formed by a long, narrow articulo-angular 
element, ornamented externally, having a nearly straight inferior 
margin, an arched superior margin in advance of the articulation, 
and exhibiting a short extension behind this facette. The small 
toothless dentary element meets this bone in front, reaching to the 
symphysis, and bounded below by a thin infradentary. A long, 
deep, laminar splenial bone, tapering in front, but with a straight 
dentigerous border in the greater part of its length, is apposed to 
the dentary and articulo-angular on their inner face ; and this forms 
the inner wall of a vacuity existing between the upper portion of 
the two outer elements. 
The robust ceratohyal on each side is connected with the hyo- 
mandibular by an elongated bone, with expanded extremities, 
which may be regarded as the stylo-hyal. This element is termed 
metapterygoid by Reis, and is supposed by that author to have 
supported a “ prseclavicular ” fin. The latter determination, how¬ 
ever, is founded upon two distorted fishes from the Ravarian Litho¬ 
graphic Stone, in the Munich Museum, which exhibit accidentally 
displaced fragments of the pectoral fin-rays at the postero-inferior 
angle of the head. 
The branchial arches are four or five in number on each side, deli¬ 
cately and deeply channelled on the hinder aspect as in Polypterus 
and modern bony fishes. So far as has been definitely observed, 
each arch consists of a single pair of much arcuated elements, in 
some genera with sparse appended bony denticles ; and a single 
large copula, with spatulate hinder extremity, unites all the lower 
extremities of the arches in the median line. 
The notochord must have been persistent, and the present writer 
has not observed any satisfactory indications of ossified elements in 
the notochordal sheath. According to Reis ] , however, hypocentra 
are distinguishable in the so-called Codacanthus Jicissice. The 
1 Op, cit. p. 70, pi. iv. figs. 15, 16, 19. 
