134 ON THE MORPHOLOGICAL CONSTITUTION OF 



bar, which is the centrum of the pre-sphenoid, and which 

 passes in front into the cartilaginous nasal septum, which 

 constitutes the ethmoidal and vomerine centrums. The 

 crocodilian and chelonian skulls are, in fact, entirely destitute 

 of ossified central elements in front of their post-sphenoidal 

 centrums, the superincumbent framework in these forms of 

 cranium being supported along the base, not by ossified cen- 

 trums, but by greatly expanded and modified pterygoids, 

 ento-pterygoids, ethmoidal neurapophyses, maxillaries, and 

 inter-maxillaries, immediately above which series of bones 

 lies the persistent central axis of the primordial cranium, as 

 far back as the ossified centrum of the post-sphenoidal sclero- 

 toine. In the mesial antero-posterior section of the macerated 

 skull of the Crocodilus vulgaris, a suture will be found com- 

 mencing in front of the common orifice of the Eustachian 

 tubes, and terminating at the lower part of the root of the 

 laterally-compressed post-sphenoidal process already alluded 

 to. In front of this suture, the' section presents no traces of 

 central elements, the pterygoids and so-called "palatals" 

 taking their places. In a section of this kind in the Museum 

 of the University of Edinburgh, the extremity of the anterior 

 process of the pterygoid passes forwards and downwards, 

 appearing in the suture between the two "palatines," about 

 an inch from their anterior margins ; the right and left por- 

 tions exposed on the vault of the palate being separated from 

 the " palatines " by surrounding suture, and forming together 

 a narrow double surface, one-eighth of an inch in length. In 

 the section to which I allude, and in similar sections, I ob- 

 serve traces of the line of anchylosis between these anterior 

 processes and the pterygoids themselves. These lines run up- 

 wards and forwards, and appear to include the anterior and 

 greater part of the pterygoidal portion of the nasal septum, 

 and the thin plate which, on each side, passes up to be 

 united to the descending process of the " pre-frontal." In 



