36 THE FROG 



213. Caudal and ventral to these are the occipitals (N), 

 bearing the condyles by which the skull articulates 

 with the atlas (228) of the vertebral column. Be- 

 tween these, on the posterior face of the skull, is the 

 foramen magnum, the aperture by which the spinal 

 cord leaves the skull. 



214. Laterad to the occipitals and articulating with the 

 fronto-parietals are the prootics (N) which cover 

 the inner ear. Note the opening, fenestra ovalis, 

 covered in life by a cartilage, with which the 

 columella (165) articulates. 



215. Laterad to the prootics are the large T-shaped 

 squamosals (tympanies) (D). 



216. At the caudal lateral margins of the squamosals are 

 the quadrato-jugals (D), which articulate with the 

 maxillaries. They form the suspension for the lower 

 jaw. 



Drawing 18. Draw the right half of the skull from 

 the dorsal aspect (x4). 



Place the skull ventral side up. Examine the lower jaw 

 and find the following bones. 



217. At the cephalic end, corresponding to the pre- 

 maxillaries, are the mento-meckelians (preden- 

 tales) (D). 



218. The long dentales (D) are just caudal to them. 

 Note the arrangement of the teeth. 



219. The angulare-splenials (D) articulate with the 

 quadrato-jugals (216) by means of the quadrate 

 cartilage (S). These derm-bones cover the Mecke- 

 lian cartilages (S) of the lower jaw. Both carti- 

 lages arise from the first (mandibular) visceral arch 

 of the embryo. 



