170 ON THE STRUCTURE OF THE SKULL. 



Furthermore, in the foetal human skull, the basi-sphenoid con- 

 tributes nothing towards the posterior boundary of the pituitary 

 fossa, which is formed by the long cartilaginous synchondrosis 

 which connects the rudimentary basi-sphenoid with the basi- 

 occipital. I identify the lamella of cartilage which I have 

 described in the Pike with this synchondrosal portion of the 

 foetal human basis cranii. 



But the basi-occipital, basi-sphenoid, presphenoid, ethmoid, 

 and vomer of Man being now accounted for in the Pike's cranio- 

 facial axis, what, it may be said, is the nature of the bone x to 

 which the term "basi-sphenoid " is commonly applied? 



It differs from any of the ossifications of the basi-sphenoidal 

 cartilage in Man, not only by extending backwards beneath 

 the basi-occipital, but by stretching forwards, beneath the pre- 

 sphenoidal and ethmoidal cartilages, to within a short distance of 

 the anterior extremity of the cranium ; and in the still more 

 important chcumstance that it is an ossification within the 

 perichondrium, which can be stripped off, in skulls which have 

 been macerated, or steeped for a short time in boiling water, 

 without injury to the cartilage upon which it is developed. 



Mr. Parker has shown, in his valuable paper on Balseniceps* 

 that the so-called basi-sphenoid of birds is developed from 

 three ossifications, a central one, the true basi-sphenoid, and two 

 lateral and inferior centres — the "basi-temporals" (Parker), 

 which appear to correspond with the lingulse of Man. 



The thought readily arises that the single bone x may cor- 

 respond with these two basi-temporal ossifications. The latter, 

 however, appear to be cartilage ossifications like the lingulse 

 themselves : and, upon the whole, I think it will be safer, at any 

 rate for the present, to regard the bone x as peculiar to the 

 branchiate Vertebrata, and to confer upon it the special name 

 of " para&phenoid." 



Connected with the bones of the basi-cranial axis are upper 

 arches, and, as in Man, the liindermost of these arches consists 

 of three elements, two of which are lateral and one superior. 

 Each lateral bone articulates below with the basi-sphenoid, and 

 forms the lateral boundary of the occipital foramen. Above, it 



* Transactions of the Zoological Society, vol. iv. 



