THE SKELETON OF THE VERTEBRATE HEAD. 155 



sphenoido-frontals near their lower extremities, and the con- 

 sequent space left between this bony bridge and the deep 

 furrow formed by the inclined upper surfaces of the ento- 

 pterygoideal portions of the pterygoids. 



In' the Lacertians. In the lizards, the sphenoido-frontal 

 is again double. In consequence of the mesial separation of 

 the ento-pterygoids ("palatals") and pterygoids, the elongated 

 fibre-cartilaginous centrum and neurapophyseal interorbital 

 laminae, are left unsupported below ; to which circumstance 

 is probably due the formation in the interorbital laminae of a 

 pair of delicate triradial osseous neurapophyses, which pass 

 off from the upper margins of the optic foramina. 



In the Ophidian and Batrachian. Leaving the further 

 consideration of the special homology of the anterior sphenoidal 

 wing in the reptiles, and more especially in the crocodiles, 

 until the posterior sphenoidal wing, and the so-called "petrosal," 

 have been examined, I would observe, that the grounds on 

 which Professor Owen distinguishes the "os en ceinture" 

 of the frog, from that segment in the python which includes 

 the so-called "frontals," appear to me somewhat arbitrary. 

 This segment in the serpent consists of a pair of neurapophyses, 

 or orbito-sphenoids, which are distinct, as cartilages at least, 

 in the embryo ; of a double meta-neurapophysis (sphenoido- 

 frontals), which not only occupy on each side the positions of the 

 neurapophyses, but extend the fore part of their inner margins 

 downwards, back to back, in the mesial plane, on the sides of 

 the compressed centrum ; which thus, along with them, 

 divides the neural chamber in front, for the transmission of 

 the olfactory nerves. The sides of the " os en ceinture " are 

 formed by neurapophyses ; while the so-called " frontals " of 

 the serpent occupy the greater part at least of the sides of 

 their segment ; in other respects, their relations are similar. 

 They are both catacentric ; the centrum, in both, resting, as 

 in the bird, on the upper surface of the anterior acuminated 



