THE STRUCTURE OF THE PIKE'S SKULL. 181 



taken together, answer to the palato-pterygoid bones of the Man ; 

 but it is a very difficult matter to identity the separate con- 

 stituents of the two arches. 



One of the most striking features of the palatine bone, not 

 only in Man, but in the Vertebrata generally, is its articulation 

 with the pre-frontal, or lateral mass of the ethmoid. If, guided 

 by this character, we seek for the homologue of the palatine in 

 the Fish, the so-called " ectopterygoid ' alone satisfies the con- 

 ditions. But if this bone be the homologue of the true palatine, 

 the bone PL must be regarded as a dismemberment, or subdivi- 

 sion of the palatine,* and the entopterygoid will take the 

 place of the true pterygoid. 



The palato-quadrate arch, with the lower jaw, is immediately 

 suspended to the skull only by the articulation of the carti- 

 laginous pedicle b (Fig. 71) with the pre-frontal, none of the 

 posterior elements of the arch being directly articulated with 

 the skull. They are indirectly united with the latter, however, 

 by two very remarkable bones, the Hyomandibular (H.M.) and 

 the Symplectic (Sy.). 



The os hyomandibular e is a broad flattened bone, somewhat 

 constricted in the middle, and divided below into an anterior 

 and a posterior process. The upper convex edge of the bone 

 (d, Fig. 71) fits into an elongated, concave, glenoidal fossa 

 bounded by the squamosal, opisthotic, and pro-otic bones, and 

 swings freely therein, in a plane perpendicular to the longi- 

 tudinal axis of the skull. The large anterior inferior process 

 articulates by its anterior edge and outer face with the meta- 

 pterygoicl, while below it is united by a persistent synchondrosis 

 with the irregular styliform bone, the SympJedic, which is firmly 

 fitted into the groove already described upon the inner face of 

 the quadrate bone. 



The connection thus established between the hyomandibular 

 and the symplectic, is strengthened externally by the firm ap- 

 position of a curved elongated bone, the Pre-operculum, to the 

 hyomandibular above and to the quadrate bone below. 



* Looking upon Fa. and Ecpt. as one bone homologous with the palatine of 

 Man, it will he found that iu osseous Fishes the separation between them takes 

 place sometimes in front of the pre-frontal articulation, as in the Pike, sometimes 

 behind it, as in the Cod and most bony fishes. 



