THE SKELETON OF THE VERTEBRATE HEAD. 183 



occupied by fibrous texture ; the " basi-sphenoid" or post- 

 sphenoidal centrum extending forwards below ; and the " pari- 

 etals" taking the place of the deficient meta-neurapophyses. 



The preceding view of the arrangement of the centrums 

 and neural arches of the post-stomal sclerotomes of the lower 

 forms of cranium, is that which would appear naturally to 

 suggest itself to a mind uninfluenced by the arrangement of 

 the corresponding region of the mammalian skull. It is 

 assumed throughout that there are more or less complete carti- 

 laginous or osseous auditory capsules in addition to correspond- 

 ing neurapophyses ; and that these neurapophyses are not 

 post-sphenoidal but temporal, as evinced by their zygopophy- 

 seal connections in the human cranium. No reference has 

 been made to the relations of the contested " petrosals" and 

 ali-sphenoids" to the fifth nerve, because, while the funda- 

 mental relation of that nerve to the post-sphenoidal sclerotome 

 is admitted, the divisions of the nerve exhibit the same 

 tendency to vary in their points of exit, as is presented by the 

 other cerebral nerves ; moving backwards more or less across 

 the corresponding neurapophyses, and notching or perforating 

 the neurapophyses behind. In fact, until a more minute 

 investigation of the development of the cranium in its relations 

 to the cerebral nerves has afforded some explanation of the 

 varied relations of these parts in the series, we cannot, in 

 my opinion, attach much weight to the determination of a 

 " petrosal" or an " ali-sphenoid" by means of their relations 

 to the trigeminal nerve. 



Proceeding now to the examination of the post-stomal 

 centrums and neural arches of the mammalian cranium, let 

 the human skull be selected for examination. The occipital 

 centrum is surmounted by a pair of neurapophyses and a 

 double meta-neurapophysis. But again, surmounting the 

 meta-neurapophyses there is a double piece, which occasion- 

 ally remains permanently separate from the " occipital bone." 



