ANATOMY OF VERTEBRATES. 129 



are defended partly by fibre-cartilage, partly by the exogenous 

 descending lamellae, 7', of the parietals : there are no separate ossifi- 

 cations answering to 9 and 10 in fishes. 1 The frontals, fio;s. 90. 91, 



O O ' 



11, are supported like an arch between the parietals 7 and pre- 

 frontals, 1 4 : and each sends down a longitudinal lamella, bound- 

 ing the sides of the narrow anterior continuation of the brain- 



o 



chamber, as in Polypterus ; but continued by an unossified plate to 

 the cartilaginous presphenoid and vomer below. The postfrontal, 

 fig. 91, 12, extends from its connections with the frontal n, and 

 parietal 7, downward and backward to unite with the mastoid, 8, 

 in the Turtle, and with the malar, 2fi, and squamosal, 27, in all 

 Chelonia. It forms the posterior boundary of the orbit, but does 

 not contribute any share to the proper cranial walls. 



The median symmetrical bone, fig. 90, 13, which, like a hypa- 

 pophysis, is developed in the lower part or production of the 

 notochordal capsule, which underlaps the anterior end of the 

 basi-pre-sphenoid, 5, by its narrow hinder part, - - expanding as it 

 advances to articulate with the prefrontals, 14, having the pala- 

 tine bones, ib. 20, abutting against the broad anterior part, and 

 entering by its under surface into the formation of the roof of the 

 mouth, fig. 98 B, n, repeats the essential characters of the bone so 

 numbered and termed f vomer ' in Fishes, figs. 81, 83, 84, 85, 13 ; 

 and, like it, represents the centrum of the foremost segment of the 

 vertebral series. The vomer is single in Chelonia, as in most fishes. 



The bones, fig. 90, 14, in neurapophysial relation with the vomer, 

 protecting the sides of the rhinencephalon or olfactory bulbs, 

 entering into the antero-superior boundary of the orbit, forming 

 part of the surface of attachment of the palatines, supporting 

 the fore part of the frontals, and connected, but more commonly 

 connate, with the nasals, ib. is, fig. 91, 14, repeat the essential 

 characters of the prefrontals of Fishes, figs. 83, 85, 1 4. Connate, as 

 in Chelonia they usually are, with the nasals, their outer expanded 

 plate unites with the maxillary, fig. 91, 21, and completes the 

 upper border of the nostril, is. 



The palatines, figs. 90, 98 B, 20, form the sides of the roof of the 

 mouth, articulating medially with the vomer, is, n, and laterally 

 with the maxillary, 21, and pterygoid, 24. The maxillary, figs. 

 90, 91, 21, presents a palatal, facial, and orbital plate. The palatal 

 plate, fig. 98 B, 21, developes a masticatory ridge parallel with the 

 sharp alveolar border. The facial plate, fig. 91, 21, shows the con- 

 nections with the prefronto-nasal, u, the premaxillary, 2-2, and the 

 malar, 26 ; the orbital plate is usually perforated by the lacrymal 



1 xxxviir. ; Tab. xxi. fig. 89, 1, r. 

 VOL. I. K 



