90 PROF. W. K. PARKER ON THE STRUCTURE OF 
above and below and winged at the middle; it is the high interparietal crest (7.p) (see 
also fig. 1). Bounding the temporal space, right and left, is the crest of the squamosal 
(sq), which rests on the supratemporal (s.¢), forking over it ; the pedicle of the quadrate 
(pd) is here cut across. 
Section 14.—Both crests are now very high (Plate XVII. fig. 6); and the inter- 
parietal (7.p) is thickest above, and tuberculate both there and in the middle; the outer 
bones are not figured. 
Section 15.—Here the section of the crest (Plate XVII. fig. 7, 7.p) is very similar to 
the last, and the squamosal (sq) has the form it showed in fig. 5; the supratemporal (s.t) 
is here cut through in its hinder part. 
The Postoral (Visceral) Arches. 
A preoral arch, the ethmo-palatine, has already been described (see Plate XVII. 
fig. 5, and Plate XVIII. figs. 6 and 6a, pa); that is a mere rudiment. Between that carti- 
lage and the quadrate bone there is no endoskeletal structure; for the “ epipterygoid ” 
is suppressed. Behind the mouth two large and one lesser arches are found. The pier 
of the mandibular arch or quadrate (Plates XVI. and XVIL., g) is one third the length 
of the mandibular ramus; its proper pedicle (pd) is free, semielliptical, and unossified 
at its end; the outer process (o¢.) is in a line with the shaft of the bone, and is 
scooped above, where the two temporal bones (sq, s.¢) rest upon it; that articulation 
has considerable mobility. This bone has a narrow waist and widened ends; the lower 
part ends in a condyle (q. ¢) like that of the cervical vertebra of a bird; in the axial 
direction it is convex ; crosswise it is hollow or saddle-shaped. The articular surface of 
the mandible (Plate XVI. fig. 1, and Plate XVII. fig. 1) is concave lengthwise, and 
convex across. ‘The proximal part of the lower jaw is ossified as the “articulare,” and 
then runs to the chin as an undiminished Meckelian cartilage, partly hidden by the 
splenial (Pl. XVII. fig. 1, ar, mk, sp). 
The hyoid arch is in four parts on each side, roughly answering to the pharyngo-, epi-, 
cerato-, and hypohyal of a normal branchial arch, besides a huge glosso- or basihyal, 
which itself is subdivided (Plates XVI. and XVIL.). 
The topmost element, or mediostapedial (m.st), is confluent with the oval stapedial 
plate (s¢); it is a very slender rod, which passes downwards and outwards. Where the 
bone ceases there the extra-stapedial region begins; but any segmentation of the 
cartilage which may have existed is gone. 
The extrastapedial (Plate XVI. fig. 7, e.st) is a large tongue of cartilage attached to 
the dzner side of the quadrate behind, in its normal ichthyic position; for there is no 
drum-cavity in this type, and therefore the extrastapedial does not ride over the edge of 
the quadrate, as in those types which have an ear-drum. ‘There is a fenestra (¢.st./) 
in the proximal part of the cartilage ; and above this space the thickened inner edge of the 
