FISHES. 21 



reptiles. In the osseous fishes there are four or five bones on each 

 side, of which the uppermost [ejntympanicum Owen) is connected 

 with the skull (with the squamosal [mastoid Owen] and posterior 

 frontal) by articulation, whilst at the upper part behind it has an 

 articular surface for the gill-cover {operculum). Under this bone is 

 a flat osseous disc, often of a circular form ; to this CuviER gives the 

 name of os tympanicum ; behind it lies a styliform bone\ and 

 under the two a triangular bony lamina with a smaller inferior 

 extremity and an articular head, which is connected with the lower 

 jaw. CuviEJi names this the jugal bone. (In the batrachians the 

 jugal bone runs from the upper jaw to the quadrate bone, and then 

 forms a portion of the articular head for connexion with the lower 

 jaw.) Behind this connecting arch there lies between the skull and 

 the lower jaw the gill-cover, consisting of various bones, of which 

 the first descends as an elongated curved bone nearly as far as the 

 lower jaw. Tl\\\ii pi-ieoperculum seems to be simply a portion of the 

 temporal bone, according to Geoffeoy Saint-Hilaire the proper 

 OS tympanicum, according to Agassiz the styliform process {proces- 

 sus stylo'ideus'^) . 



The ujjper jaw-bones are commonly without teeth, and lie in 

 the upper lip; they run obliquely backwards and downwards, with- 

 out being connected at the extremity with other bones. The inter- 

 maxillary bones are, on the other hand, usually armed with teeth ; 

 as are also the palate-bones, which are situated at the sides of the 

 vomer. Behind each of these palate-bones lie two bones which are 

 attached by cartilage to the jugal bone and the lamelliform middle 

 portion of the quadrate bone, and may be aptly compared with the 

 pterygoid processes that divide into an external and internal wing^. 



Below tlie orbits of the eye is placed a row of bony scales, 

 quite external, which form a half-ring connected behind with the 

 anterior frontal bone. Some writers regard these bones as parts of 

 the jugal bone; but they belong perhaps to the dermal skeleton, 

 and thus may be compared with the aj)paratus of the lateral line 



1 Os symplecticum CuviER, Tympano-malleale Agassiz, Meso-fympanicuni Owen. 



2 [Owen Homologies, p. 65. The opercular bones have no special homologues in 

 higher animals. They form collectively the diverging appendage of the descending or 

 tympano-mandibular arch of the third cranial vertebra.] 



3 [Owen Homologies, p. 114. The diverging appendage of the maxillary arch of 

 the fourth, or anterior, vertebra of the head.] 



