214 report— 1846. 



sphenoid (6). In most lizards the wider roof of the cranium, supported by the 

 long mastoids, squamosals, postfrontals and malars, like a bony scaffolding 

 on each side, is independent of its proper (neurapophysial) walls for support, 

 and these retain, through the ceconomy of nature, their primitive semi-mem- 

 branous, semi-cartilaginous state. A dismemberment of the alisphenoid 

 (which may be discerned as a process of that bone in the piscine genera 

 Xiphias, Sphyrcena) props up the parietal upon the pterygoid, so like a post 

 or pillar, that the name 'columella' may well be retained for it. At the 

 sides of the membrane forming the orbital aperture, rudiments of the orbi- 

 tosphenoids may be seen in most lacertia : I find them, e. g. in the form of 

 a slender osseous filament on each side, slightly bent inwards and bifurcate 

 above, in a large Australian lizard ( Cyclodus gigas). In the crocodile (figs. 

 9, 20, and 22, 10) the orbitosphenoids attain their maximum of development, 

 but retain all their typical characters : they bound the orbital aperture of the 

 cranium ; are notched below, as in many fishes, by the optic nerves (op) ; 

 are perforated by the pathetic and other orbital nerves at the ' foramen spheno- 

 orbitale' (s) ; they protect the sides of the prosencephalon ; support above the 

 frontals (and by their backward development also the parietals) ; and they 

 rest below upon a peculiar development of the presphenoid (9), which seems 

 to answer to the entosphenoid in fishes. 



Some salient points of resemblance between the cranial organization of fishes 

 and birds have elicited remarks from more than one comparative anatomist. 

 Not to dwell upon the more obvious correspondence arising out of the mo- 

 bility of the upper jaw, chiefly through its connection with the pedicle of the 

 lower jaw, I may indicate the overhanging position of the orbitosphenoid 

 (figs. 8, 23, 10), raised high above the presphenoid (9), at the back part of the 

 interorbital septum : we see exactly the same position of the orbitosphenoid 

 in many fishes. Cuvier accurately represents it in the skull of the perch*. 

 This beautiful trait of unity of organization is completely put out of sight by 

 the false homology of the orbitosphenoid in fishes with the alisphenoid in 

 birds and mammals. The progressive recession of the orbitosphenoid and 

 alisphenoid, as we descend from mammals to fishes, transfers indeed their 

 characteristic nerve-notches or foramina from their posterior to their ante- 

 rior margins. But the notch (op, fig. 8) at the posterior margin of the orbito- 

 sphenoid in the bird for the escape of the optic nerve by a foramen common 

 to it and the nerves of the orbit, is not less significant of its true homology 

 than is the anterior notch in the crocodile or fish ; the osseous connections 

 with the sphenoid below, with the frontal above, and with the alisphenoid 

 behind, being the same. 



Prefrontals. — If the cranium of a cod-fish be bisected horizontally and 

 longitudinally, its most contracted part will be found at the upper part of 

 the interorbital aperture, bounded by the orbitosphenoids, which mark the 

 division between the prosencephala and rhinencephalic compartments of the 

 cavity : the latter extends as a triangular channel or groove on the under 

 part of the frontal, opening below into the orbits, gradually expanding as it 

 advances forwards, and dividing into two canals, which diverge to the inter- 

 spaces left on each side of the nasal, between it and the bones (fig. 4, 14), that, 

 meeting behind the anterior expanded end of the nasal, bound the anterior 

 extremity of the true and entire cranium. The diverging canals of the rhi- 

 nencephalic compartment are formed by the two bones in question: the rhinen- 

 cephalaor olfactory ganglions are sometimes lodged at the extremities of these 

 canals, and they send out the olfactory nerves by the apertures formed be- 

 tween the bones 14 and 15, which then ramify upon the vascular olfactory sacs, 

 * Histoire des Poissons, pi. ii. figg. i. vii. 14. 



