1894.] 



HTOID ARCH OF CERATODUS. 



633 



The hypohyal (figs. 1 and 2, hh) is paired, cartilaginous, and 

 isodiametric, and the two hypohyals are applied to one another in 

 the middle line hy flat, vertical, articular surfaces which open out 

 in front to receive the wedge-shaped posterior extremity of the 

 basihyal. 



Fig. 2. 



bh hh ch 



Ceratodus forsteri. — Hinder portion of the skull with the hyoid arch ; left side. 

 The opercular and interopercular bones are removed, bh, basihyal ; 

 hh, hypohyal ; ch, ceratohyal ; hm, hyomandibular ; hsp, hyosuspensorial 

 ligament ; sg, squamosal or pre-opercular ; qu, quadrate condyle ; oe, 

 eye-capsule. 



The basihyal (figs. 1 and 2, bh) is a median unpaired cartilage 

 which tapers off to a blunt point in front. 



In Giinther's (4) original description of Ceratodus the hypohyals 

 are called basihyal, while the figures, and the words (p. 526) " the 

 basihyal is short, thick, cartilaginous, interposed between the ends 

 of the ceratohyals and the acutely conical glossohyal," fail to indi- 

 cate the paired nature of these cartilages. Seeing, however, that 

 they are paired and that the term basihyal is always applied to a 

 median copula, and seeing that they are, from their relation to 

 the ceratohyal, evidently homologous with the hypohyals of the 



