320 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 



N.B. These are amongst the most constant cranial elements in all the Vertebrata, 

 and are the most important of the ' periotics.' 



3. The anterior infero-lateral elements — the ' ali-sphenoids.' 



N.B. These elements are very constant in Mammals and Birds. They are large 

 in the Crocodilia, but feeble and inconstant in the rest of the Abranchiate 

 Reptilia. They are not ossified in the Batrachia, and are generally very small 

 in osseous Fishes. 



4. The supero-lateral elements — the ' squamosals.' 



N.B. These elements are large and well-developed in Mammalia, Birds, and 

 Abranchiate Reptiles; they are scarcely differentiated in the Batrachia, and 

 they are large and constant in the osseous Fishes. 



5. Upper elements — the ' parietals.' 



N.B. These are very constant throughout the Vertebrata, but are separated from each 

 other in certain Carnivora, and in some osseous Fishes, by the inter-parietal. 



TTie Pre-sphenoidal Sclerotome. 



1. The centrum or basal part — the ' pre-sphenoid'.' 



N.B. This element, distinct and normal in the Mammalia, is high and com- 

 pressed in Birds. It is not ossified, as a rule, in the Reptilia, but, according 

 to Goodsir, forms part of the bony septum of the ' os en ceinture ' in Snakes 

 and Frogs : it has no distinct osseous representative in Fishes ; the interorbital 

 septum in this latter class being an orbito-pre-sphenoid. 



2. The infero-lateral elements— the ' orbito-sphenoids.' 



N.B. These elements — usually well-developed in the Mammalia, but extremely 

 feeble in the Mole — are short and connate in Birds even when they have 

 a distinct osseous centre^, which is not always the case. In the Chelonia, 

 Crocodilia, and Lacertiiia they are fibro-cartilaginous, and appear to have no 

 centre of their own in the Ophidia and Batrachia. They are generally 

 unossified in Fishes. 



3. The supero-lateral elements — the ' post-frontals.' 



N.B. These elements are exogenous in Mammals, and, with one or two rare excep- 

 tions, they are not distinct in Birds. They are well developed in Crocodiles, 



' In our description of tlie pre-spheuoid we have followed Professor Goodsir {op. cit. p. Ii4) ; if, however, 

 Cuvier, Hallman and Huxley be right, not only the detached ossifications anterior to the 'hinge,' but also the 

 upper and anterior portion of the great inter-orbital ossification, is essentially ethmoidal in its nature. 



' Dr. Hallman (Die Vergleichende Osteologie des Schlafenbeins, PI. I. fig 2) represents the Goose as having 

 a distinct V-shaped osseous centre for the orbito-sphenoids. In the African Ostrich there is one large osseous 

 centre, an ' orbito-pre-sphenoid ' exactly as in the Carp ; whilst in the young Emeu of the sixth week after 

 hatching, the posterior margin of the orbito-pre-sphenoidal cartilage is already ossified, — a condition precisely 

 like what is seen in the half-grown Pike. Recent observations on Birds scarcely mature have yielded us u 

 distinct osseus pre-sphenoid, with exogenous orbital alse, in very many species : its absence is quite exceptional. 



