The clavicles are the haemapophyses of the atlas : the haemal spine is confluent with the constricted centrum : the pleurapophyses are short and stunted. Let their homologues in the echidna or in birds be examined. Who can deny the strong resemblance between the furcular bone, and those wedge-shaped bones, which form the haemal canal for the protection of the artery which runs along the inferior surface of the caudal vertebrae in the kangaroo, the ferret, or the beaver ?
The second cranial vertebra (parietal) surrounds the mesencephalon, in which there is included part of the pons varolii, the optic lobes, or nates and testes, and the pituitary body: all these parts are covered in man by the highly-developed cerebral hemispheres. The basi-sphenoid (centrum) is that primitively distinct portion of the sphenoid bone, which lies between the basilar process of the occipital bone behind, the process olivaris of the sphenoid in front, and the two great alae of the sphenoid on either side. The excavation for the pituitary body, and the prominent points of bone termed the posterior clinoid processes, give rise to the appearance, which, from its resemblance to an eastern saddle, has been designated sella turcica. The neu-rapophyses (alisphenoids) are represented by the great wings of the sphenoid bone. They soon coalesce with the basi-sphenoid, and are perforated at their bases by the foramina (rotunda and ovalia) for the transmission of the second and third divisions of the trigeminal nerve.
The alisphenoids are pushed forwards from the occipital vertebra by the intercalation of the mastoid, squamosal, and petrosal bones, the coalesced assemblage of which constitutes the so-called temporal bone; but they maintain their connection with their proper neural spine (the two parietal bones), even in those skulls where the receding frontal bone would seem to push the parietals backwards towards the occiput.