3 86 



MANUAL OF ELEMENTARY ZOOLOGY 



The skulls of reptiles are complicated structures. They contain less 

 cartilage than those we have dealt with as yet, and the arrangement of 

 the bones is of interest in several ways, (i) In the occipital region, 

 there are, as well as the exoccipitals at the sides, a supraoccipital above 

 and a basioccipital below, and (except in some extinct forms) a single 

 occipital condyle underneath the foramen magnum replaces the two 

 lateral ones of the frog. We shall see later that birds have one condyle, 

 and mammals two. (2) The frontoparietals of the frog are usually 

 represented here, as in most other vertebrates, by separate frontal and 

 parietal bones. Prefrontals and postfrontals lie at the corners of the 

 frontals. . (3) In most cases (not in snakes) the forepart of the cranium 

 is so compressed between the eyes that its hollow disappears, and it 

 is replaced by a vertical sheet of membrane, the interorbilal septum, 

 so that in the dried skull the two orbits open widely into one another. 



c.car C i S Ing. 



Fig. 279. — Semi-diagrammatic views of the arterial arches. 



A , o f a salamander ; B , of a common newt. 



-4, Vessels of the first to fourth branchial arches ; c.gl., carotid gland ; car., caro- 

 tid arch; c.car., common carotid artery; coel., cceliac artery; d.ao., dorsal 

 aorta; d.ar., ductus arteriosus; Ing., lingual artery;/., pulmonary artery; 

 pul., pulmonary arch; tr., truncus arteriosus; scl., subclavian artery; sy., 

 systemic arch. 



The sphenethmoid of the frog is not found. (4) The quadrate 

 cartilage of the frog is replaced by a quadrate bone, with which the 

 lower jaw articulates. This bone is found in birds, but not in mammals, 

 where the lower jaw articulates with the squamosal. (5) Except in 

 turtles a transpalatine bone joins the maxilla to the pterygoid. (6) The 

 true cranium is not large, but processes from certain bones of the 

 hinder part of it, with others which do not touch it, form a scaffolding 

 about it which supports the jaws, and upon which the skin of the head 

 is stretched. This is the remains of a complete false roof of dermal 

 bones found in the Stegocephali (p. 384). Between the bars of the 

 scaffolding are spaces known as fossa. The scaffolding is most perfectly 

 developed in the tuatara. Here there are two longitudinal bars or 

 arcades strutted out from the skull by two transverse bars. The bars are 

 composed as follows : (i) The upper or supratcmporal arcade, parallel 

 with the parietal region of the cranium, of the postorbital and squamosal 

 (in other reptiles the postorbital becomes a part of the postfrontal) ; 



