XXIII] LACERTA VIV1PARA 57 1 



sternum corresponds to the sternum of Amphibia, but the forks 

 behind, which are termed sternal bands, are formed by the union 

 of the ventral ends of the sternal ribs of one side with one another. 



The skull is distinguished from the Amphibian skull by many 

 features. The jaws do not arch outwards at the sides of the 

 cranium, as in the Frog, but are bent inwards underneath it. 

 Behind, the cartilage of the cranium is completely replaced by 

 four bones by the supra-occipital above the foramen magnum, 

 the exoccipitals at the sides of this opening, and the basi-occipital 

 beneath. This last bone bears a single knob or condyle which 

 articulates with the atlas vertebra. To the formation of this 

 condyle the exoccipitals in some degree contribute. The basi- 

 occipital and the single condyle are highly characteristic of all 

 Reptilia. In common with all Amniota Reptilia possess a supra- 

 occipital and abasisphenoid bone. The last-named is a bone re- 

 placing the cartilaginous floor of the cranium just in front of the 

 basi-occipital. The parasphenoid so characteristic of Amphibia is 

 reduced to a mere splint attached to the front of the basisphenoid. 



The anterior part of the cranium is so compressed between the 

 large eyes that its cavity completely disappears and it becomes re- 

 placed by a vertical sheet of membrane, the interorbital septum. 

 It follows that in the dried skull the two orbits apparently open 

 widely into one another. Almost the entire brain is pushed back 

 behind the eyes into the hinder part of the cranium. Only the 

 olfactory stalks run through holes in the upper part of the septum. 

 The orbitosphenoid of Urodela and the sphen ethmoid of the Frog 

 are quite unrepresented, though in some of the larger Lizards allied 

 to Lacerta there is a minute orbitosphenoid bone in the upper part 

 of the interorbital septum (31, Fig. 281). The interorbital septum 

 is certainly a characteristic of the primitive Reptilia. It has how- 

 ever been lost in some of the most recent and highly modified forms. 



The auditory capsule as in Teleostei is completely converted 

 into bone, but it is ossified by three bones only, an epi-otic above, 

 which fuses with the supra-occipital, an opisthotic behind, which 

 joins the exoccipital, and a pro-otic which remains distinct. 

 There is no trace of the pterotic bone so characteristic of Teleostei. 



As in Amphibia the first visceral arch is represented by an upper 

 half consisting of a suspensorium with a pterygoid process, and a 

 lower half Meckel's cartilage. In the upper half, however, the 

 cartilage is completely replaced by bone. The suspensorial portion 

 forms the quadrate bone, which is attached to the side of the 



