In front of the basi-occipital the base of the skull is formed by the _basisphenoid_ (_parasphenoid_ of Huxley) (6). This very long and narrow bone extends from the basi-occipital beyond the brain-capsule to between the orbits, where it forms the support of the fibro-membranous interorbital septum. Anteriorly it is connate with another long hammer-shaped bone (16), the _vomer_, the head of which marks the anterior end of the palate, and is beset with teeth. The _alisphenoids_ (11) are short broad bones, rising from the basisphenoid; their posterior margins are suturally connected with the anterior of the basi- and exoccipitals. [Illustration: Fig. 23.--Skeleton of the Perch.] [Illustration: Fig. 24.--Skeleton of a Perch’s Skull.] [Illustration: Fig. 25.--Hyoid arch, branchial apparatus, and scapulary arch of the Perch.] [Illustration: Fig. 26.--Lower view of Skull of Perch.] [Illustration: Fig. 27.--Hyoid bone of the Perch.] The formation of the posterior part of the side of the skull is completed by the _mastoid_ and _parietal_ bones. The former (12) projects outwards and backwards farther than the paroccipital, forming the outer strong process of the side of the cranium. This process lodges on its upper surface one of the main ducts of the muciferous system, and affords the base of articulation to a part of the hyomandibular. Its extremity gives attachment to the strong tendon of the dorso-lateral muscles of the trunk. The _parietals_ (7) are flat bones, of comparatively much smaller extent than in higher Vertebrates, and separated from each other by the anterior prolongation of the supraoccipital. The anterior wall of the brain-capsule (or the posterior of the orbit) is formed by the _orbitosphenoids_ (14), between which, superiorly, the olfactory nerves, and inferiorly, the optic, pass out of the cranium. In addition to this paired bone, the Perch and many other fishes possess another single bone (15),--the _os sphenoideum anterius_ of Cuvier, _ethmoid_ of Owen, and _basisphenoid_ of Huxley; it is Y-shaped, each lateral branch being connected with an orbito-sphenoid, whilst the lower branch rests upon the long basal bone. A cartilage, the substance of which is thickest above the vomer, and which extends as a narrow stripe along the interorbital septum, represents the _ethmoid_ of higher Vertebrata; the olfactory nerves run along, and finally perforate it.