54 



TH^ SKELETON OF THE FROG. 



feet, there l^eing one large anterior fontanelle, and 

 two smaller posterior fontanelles, which are closed by 

 membrane only. In the cartilage are developed carti- 

 lage-bones, and around it membrane-bones. 

 To study the cranium satisfactoyily, the membrane-hones should 

 be stripped from one of the skulls you have p)yepared for yourself. 



a. Cartilage-bones of cranium. 



i. The exoccipitals are two irregular bony masses at 

 the sides of the posterior end of the skull. They 

 almost completely surround the foramen magnum 

 or entrance to the cranial cavity ; and bear on 

 their posterior surfaces the occipital condyles, 

 two oval convex processes which articulate with 

 the first vertebra or atlas. 



Fig. 9. The frog's skull, from the ventral surface. 



a, parasphenoid : c, columella : e, exoccipital : f.p, frontoparietal : 

 m, maxilla : ?i, vomer : o, pro-otic : _?;, pterygoid : pa, palatine : 

 pm, jjremaxilla : q, quadratojugal : se, sphenethmoid. 



ii. The sphenethmoid or girdle-hone is a bony tube 

 which encircles the anterior end of the cranial 

 cavity, and extends forwards into the olfactory 

 region : in front it is divided by a vertical partition 

 into right and left cavities, in which lie the 

 olfactory sacs. 



b. Membrane-hones of cranium. 



i. The fronto-jparietals are two long flat bones on the 

 top of the brain-case, covering the fontanelles. 



