THE OPHIDIA. 237 



the frontal region, but extend inwards below, and meet in 

 the middle line, above the basisphenoidal rostrum and the 

 persistent trabeculas. The " parietals " unite sviturally 

 with the basisphenoid. These relations are not usual 

 in true frontals or parietals (though the latter unite with 

 the basisphenoid in Chelonia, and the frontals unite in 

 the middle line of the iioor of the skull in some Mammals) ; 

 and as there are only two bones in the place of four in 

 this region of the skull, it becomes a matter for inqiiiry 

 whether the two bones, on each side, respectively repre- 

 sent orbitosphenoids + frontals, and alisphenoids + 

 parietals; or whether they represent overgrown frontals 

 and parietals only; or whether, lastly, they are the result 

 of an excessive development of the orbitosphenoids and 

 alisphenoids, true frontals and parietals being absent. 

 According to Rathke's elaborate investigation into the 

 development of the skull in Coluber natrix, the two bones 

 on each side are formed from single centres of ossifi- 

 cation, which appear in patches of "cartilage," which 

 are situated, at first, in the superolateral regions of the 

 skull, in the place normally occupied by orbitosphenoids 

 and alisphenoids, and that these grow up and meet in the 

 middle line. In this case the bones in question are orbito- 

 sphenoids and alisphenoids, and Ophidia have no true 

 frontals or parietals ; but the existence of so remarkable a 

 deviation from the ordinary construction of the vertebrate 

 skull cannot be admitted until the development of the 

 Snake's skull has been carefully re-examined. 



The Ophidia usually possess well-developed postfrontals, 

 and they have large membrane bones in front of the orbit, 

 which lie upon the cartilaginous nasal chambers, and are 

 ordinarily regarded as lachrymals. Large nasals lie upon 

 the upper surface of the nasal capsule between the lachry- 

 mals ; and, forming the floor of the front part of the nasal 

 chamber, on each side, is a large concavo-convex bone 

 ( Tl, Fig. 72), which extends from the ethmoidal septum to the 

 maxilla, protects the nasal gland, and is commonly termed 

 a turbinal, though, if it be a membrane bone, it does not 



