SKELETON OF COMMON PERCH. 



This skeleton is well ossified. The parts of the skull may be most 

 readily identified with the help of Figs. 8 and 9. The occipital region 

 (Fig. 8) is composed of the four typical bones, the supra-occipital (S.O.\ 

 which, as usual, is here of very large size; the two ex-occipitals (S.O\ which 

 surround the foramen magnum, each pierced by the glossopharyngeal and 

 vagus nerves (X.} and offering an oblique facet (*)"for articulation with the 

 first vertebra ; and a basi-occipital (B.O.\ which has a cup-shaped posterior 

 surface and articulates with the same vertebra. The basi-sphenoid (B.S.) is 

 small and has the Y-shape typical of Teleostei'. the ali sphenoid (A.S.) is 

 placed in front and above it. Between the occipital and basi-sphenoidal re- 

 gions intervenes the auditory capsule, which in Teleostei is very large and ossi- 

 fied from five centres. The bones corresponding to these centres are the epi- 

 otic (Ep. O.\ the opisth-otic (Op. O.\ to which are attached the upper and 

 lower extremities of a forked bone, the post-temporal scale (not shown in the. 



S.O. 



-Ep.0. 



PMx 



t X. 



FIG. 8. From a specimen (natural size). 



figure) by which the fore-limb is connected to the skull : the pro-otic (Pr. O.\ 

 a large bone pierced by the fifth and seventh (VII) nerves, and two bones 

 which attain their relative maximum development in the Teleostei, the 

 pter-otic (Pt. <9.), and the sphen-otic (Sp. O.\ ( = post-frontal of Huxley). 

 Between these two bones above, and the pro- and opisth-otic below, are the 

 articular cavities (t) for the two heads of the hyomandibular (H.M. in Fig. 9). 

 As is often the case, the parietal (P.) is a very small bone, and the frontal 

 (F.) a very large one. The nasal (Na.) is slender. In front of the ali- and 

 basi-sphenoid a cartilage plate, the interorbital septum (/.<9.), divides the 

 two orbits. It represents the prae- and orbito-sphenoid regions. Anteriorly 

 to the septum is a large bone, the ecto-ethmoid (E. Et.) ( = the pre-frontal of 

 Huxley), the homologue of the lateral masses of the ethmoid in a mammal, 

 and pierced by the single olfactory foramen (/.). The two ecto-ethmoids 

 are separated by a small median mesethmoid. The praemaxilla (P. MX.) 



