90 PEOr. W. K. PARKER ON THE STRUCTURE OP 



above and below and winged at the middle ; it is the high interparietal crest (i.j)) (see 

 also fig. 1). Bounding the temporal space, right and left, is the crest of the squamosal 

 (sq), which rests on the supratemporal (s.t), 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 (i.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, i.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. 



T/ie Postoral (Visceral) Arches. 



A preoral arch, the ethmo-palatine, has already been described (see Plate XVII- 

 fig. 3, and Plate XVIII. figs. 6 and 6a, jm) ; 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 XVII., q) is one third the length 

 of the mandibular ramus; its proper pedicle (pcZ) is free, semielliptical, and unossified 

 at its end; the outer process (o^.jj) is in a line with the shaft of the bone, and is 

 scooped above, where the two temporal bones (sq, s.t) rest upon it ; that articulation 

 has considerable mobility. This bone has a narrow waist and vddened ends ; the lower 

 part ends in a condyle (q. c) 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 (PI. XVII. fig. 1, ar, mic, sj}}. 



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 XVII.). 



The topmost element, or mediostapedial (m.st), is confluent with the oval stapedial 

 plate (st) ; 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 inner 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 (e.st.f) 

 in the proximal part of the cartilage ; and above this space the thickened inner edge of the 



