B04 THE ANATOMY OF VERTEBRATED ANIMALS. 



two bones in the place of four in this region of the skull, it 

 becomes a matter for inquiry whether the two bones, on each 

 side, respectively represent orbitosphenoids + frontals, and 

 alisphenoids + parietals ; or whether they rejDresent over- 

 grown 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 devel- 

 opment of the skull in Coluber natrix^ the two bones on each 

 Bide are formed from single centres of ossification, which ap- 

 pear in i^atches 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 orbitosphenoids 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 reexamined. 



The Ophidia usually possess well-developed post-frontals, 

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

 which lie upon the cartilaginous nasal chambers, and are or- 

 dinarily regarded as lachrymals. Large nasals lie upon the 

 upper surface of the nasal capsule between the lachrymals ; 

 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, pro- 

 tects the nasal gland, and is commonly termed a turbinal, 

 though, if it be a membrane-bone, it does not truly correspond 

 with the turbinals of the higher Yertehrata. The squamosals 

 are usually well developed. There is no jugal, or quadrato- 

 jugal. 



Though the general conformation of the skull in the Oj^hid- 

 ^a is that w^iich has now been described, it presents remark- 

 able modifications in different members of the order, especially 

 in the form and disposition of the bones of the jaws. In the 

 great majority of the Ophidia^ the elongated palatine bones 

 have their long axes longitudinal, lie on the outer sides of the 

 internal nasal apertures, and do not enter into the formation 

 of the posterior boundaries of those apertures. Each is con- 

 nected by a transverse bone with the maxilla, which lies at the 

 side of the oral cavity ; and the pterygoids diverge posteriorly 

 toward the quadrate bones, with which they are connected by 

 ligaments. 



