902 



SUB-KINGDOM VERTEBRATA. 



the sides of the basioccipital we have the two exoccipitals, forming 

 the lateral boundaries of the foramen magnum, and either alone or 

 in conjunction with the basioccipital, the single or double occipital 

 condyles, by which in the higher forms the cranium articulates with 

 the atlas vertebra. The bony auditory capsule is composed typi- 

 cally of the prootic, epiotic, and opisthotic, 1 to which in Teleostean 

 Fishes must be added the sphenotic and pterotic ; but, as will be 

 noticed below, some of these bones may unite, when they receive a 

 distinct name. The alisphenoids and orbitosphenoids are paired 

 bones developed in the trabecular region ; while the single ethmoid 

 and the paired turbinals occur in the nasal region. The position 

 of the quadrate has been already mentioned. Among investing or 



Fig. 824. — Upper surface of the cranium of a Labyrinthodont Amphibian (Nyrania), one-half 

 natural size, im, Premaxilla ; m, Maxilla ; N, Nasal ; L, Lachrymal \f, Frontal ; Pf, Prefrontal ; 

 y, Jugal ; Qy, Quadratojugal ; e/>, Opisthotic ; OS, Supraoccipital ; Sq, Squamosal; Squ, 

 Supratemporal ; Pa, Parietal ; Ptf, Postfrontal ; Pto, Postorbital. The quadrate would come 

 below Qy ; the large vacuities are the orbits ; and the small aperture in Pa the parietal fora- 

 men. (After Fritsch.) 



membrane bones, which are of a more or less splint-like structure, 

 we have the following paired ossifications, reckoning from before 

 backwards, on the upper surface — viz., premaxilla (im), maxilla (m), 

 nasal (TV), lachrymal (L), frontal (/), prefrontal (Pf), postfrontal 

 (Ptf), postorbital (Pto), parietal (Pa), supratemporal (Squ), and 

 squamosal (Sq). In some Dinosaurian Reptiles, as Stegosaurus, 

 there appears to be a distinct bone above the orbit, which connects 

 the pre- and postfrontal, and may be termed the supraorbital. The 



1 Shown in the skull of Testudo, figured in the sequel, fig. 1017A. 



