156 THE ANATOMY OF VEETEBKATED ANIMALS. 



The palato-quadrate and hyoraandibulai- have essentially 

 the same structure and arrangement as in Lepidosteus 

 and Aiiiia. The homologue of the suspensorium of the' 

 Elasmohrancliii is articulated with a surface furnished to it 

 by the postfrontal, pterotic, and pro-otic bones. Usually it 

 moves freely upon that sm-face, but, in the Fledognathi, it 

 may be fixed. It ossifies so as to give rise to two bones : an 

 upper broad hyomandibular (H.M.), with which the opercialuni 

 articulates; and a lower styliform symplectic (8y.), which 

 fits into a groove on the inner and posterior surface of the 

 quadrate, and is firmly held there. 



The palato-quadrate arch is represented by several 

 bones, of which the most constant are the palatine (PI.) 

 in front, and the quadrate (Qu.) behind and below. Besides 

 these there may be three others : an external, ectopterygoid 

 (Ecpt.), an internal, entopterygoid {Ept.), and a metaptery- 

 goid [Mpt.). The last envelopes the upper and posterior 

 portion of the primitive quadrate cartilage; and, fixing 

 itself against the hyomandibular, contributes to the firm- 

 ness of the union already effected by the symplectic. 



Meckel's cartilage (Mck.) persists throughout life, but the 

 ossification of its proximal end gives rise to an os articulare 

 in the lower jaw. To these an angular [An.) and a dentary 

 (D.) membrane bone are commonly added (Fig. 47). 



The hyoidean arch is usually composed of two large 

 cornua — connected with the cartilaginous interval between 

 the hyomandibular and the symplectic by a stylohycd ossi- 

 fication, and abutting, in the middle line below, upon one or 

 more median pieces, the anterior of which (entoglossal) sup- 

 ports the tongue, while the posterior (urohycd) extends back 

 to join the median elements of the branchial apparatus. 

 The cornua themselves are usually ossified into four pieces : 

 an upper (epihyal) and a lower (ceratohyal) large ossification, 

 and two small ones (hasihyals) connected with the ventral 

 ends of the lower large ossification. 



There ai'e usually five pair of branchial arches connected 

 by median ventral ossifications. The posterior pair are 

 single bones, which underlie the floor of the pharynx, bear 



