20 CLASS XIV. 



are separated from each other by a memlbranous part {fontanelle) , as 

 in Orthagorisciis. 



Under the small or anterior wings of the sphenoid and the 

 sphenoid, there is situated in the perch and many other osseous 

 fishes an unpaired bone, which divides above into two arms and 

 rests upon the body of the sphenoid below. Cuvier names this 

 part anterior sphenoid {rostrum ossis sphceno'idei, splieno'ide ante- 

 rieur) . More justly, as Agassiz determines, may it be regarded as 

 the fethmoid bone; in many fishes it remains cartilaginous. Above 

 it joins the anterior and the large wings of the sphenoid K In front 

 of this and below the anterior portion of the frontal bones lies the 

 nasal bone, a single bone, which is commonly described as the 

 £ethmoid (by Bojanus as the crista cetltmoidalis) . On each side of 

 this are situated the so-named anterior frontal bones {frontalia ante- 

 riora), which are small and closely connected with the nasal bone. 



An interposed bone ios interccdare) may be observed on each 

 side of the skull under the parietals and the external occipitals, 

 which was named mastoid [os masto'ideum) by CuviER. Often it 

 is produced into a point at the back part of the skull. It may be 

 compared to the squamous portion of the temporal bone, since the 

 external occipital is rather to be regarded (p. 19) as the mastoid'^. 

 In this bone there is often on the inferior part a small bony piece, 

 which is attached to the lateral occipital bone. It is present in the 

 perch, for instance, but is absent in the pike. Cuvier supposes it 

 to correspond with the petrous bone, which we think is not present 

 in osseous fishes ^; it is an accessory of the squamous portion of the 

 temporal. Other parts of the temporal bone, which relate to the 

 articulation of the lower jaw, belong to the bones of the face. 



The cranium is connected with the lower jaw on each side by a 

 belt of different bones, which collectively make up the articular 

 portion of the temporal bone. In the sharks and rays there is only 

 a single cartilage on each side [susjyensorium), which corresponds 

 with the quadrate bone {os quadratum s. tympanicum) of birds and 



^ [Owen names this bone entospheno'id, as the common base of the two orbito- 

 sphjeno'ids : it is peculiar, as a distinct bone, to fishes. See Homologies, p. 44.] 



2 [According to Owen the squamosal is normally absent in fishes. Homol. p. 62 

 With Owen as well as Cdvier the bone in question is the mastoid.] 



3 [See Owen Homologies, p. 28. The petrosal is the capsule of the labyrinth, and 

 is never entirely ossified in fishes; if so, it belongs to the splanchno-skeleton.] 



