FISHES. 19 



middle, and corresponds to the squamous portion of the occipital 

 bone (crista occipitalis) . It often separates the two parietal bones 

 above, whence it was named by CUVIER the interparietal bone. At 

 the side of this bone and above the lateral occipitals on each side 

 is a small bone, which is also usually referred to the occipital bone, 

 the os occipitale externum of CUVIER. BOJANUS regarded this bone 

 as the petrous bone, because one of the semicircular canals of the 

 labyrinth is covered by it 1 . But this circumstance affords no 

 sufficient ground for such a determination, since, on account of their 

 great development, the semicircular canals of fishes may be pro- 

 tected by different bones. I rather suppose, with HALLMANN, that 

 it is a part of the temporal bone 2 . Above the body of the sphenoid 

 bone and immediately in front of the lateral occipital bones, there 

 lies a flat bone on each side, ordinarily very large, and presenting 

 a foramen or notch, through which the second and third branch of 

 the fifth pair of nerves pass. These bony plates are the large alse 

 of the sphenoid (os alisphcenoideum OWEN 3 ). On the skull above lie 

 the two parietal bones, which ordinarily are small. Only rarely do 

 they meet in the middle of the head at the upper part in a sagittal 

 suture, as in Cyprinus. 



More in front, above the body of the sphenoid (which with 

 OWEN we regard as formed of the bodies of two vertebrae), are the two 

 small wings of the sphenoid (orlito-sphcenoidea) , which follow upon 

 the anterior margin of the large wings and mount up to the frontal 

 bones. Under these wings through a membranous part the optic 

 nerves proceed from the skull to the capsule of the eye. There are 

 ordinarily two large frontal bones, distinguished by a median suture, 

 which from the parietals and the occipital bone become narrower 

 forward. Sometimes they are united to form a single bone, as in 

 the haddock and the cod; in some a crest is found here in the mid- 

 line, which is a continuation of the occipital crest 4 ; sometimes they 



1 BOJANUS Anatome Tcstud. Europ. p. 171. 



2 [OWEN, parapophysis of the epencephalic vert., corresponding to the jugular 

 process of the human occipital bone.] 



3 MECKEL names this bone os petrosum, in which also HALLMANN and STANNIUS 

 concur. On its inner surface, at the inferior margin, lies the sac of the membranous 

 labyrinth. 



4 As in Lampris guttatvs, Zeus lunaGvxLL., BAKKEB 1. 1. p. 171, Tab. n. fig. in. a, 

 in Vomer, &c. 



22 



