THE SKELETON OF THE NEWT. THE CRANIUM. 141 



the case also in the frog, pierced by holes or fontanelles, and 

 these are so large that the main part of the roof and floor 

 comes to be formed by membrane bone. 



Two pairs of large ossifications take place in the cranial 

 walls. Of these the more posterior on each side represents 

 the exoccipital and all three periotic bones. It bears a 

 small convex patch of cartilage for articulation with the atlas, 

 and with its fellow forms the boundary of the foramen magnum. 



Two foramina pierce the exoccipital just in front of the 

 occipital condyle and transmit respectively the glossopharyngeal 

 and pneumogastric (fig. 21, X) nerves. Lying laterally to 

 these nerve openings is seen a patch of cartilage, the stapes, 

 which is homologous with the stapes or proximal element of 

 the columellar chain in the frog. Further forward in front of 

 the stapes is the small opening for the exit of the facial nerve, 

 and seen in a lateral view close to the orbitosphenoid, that 

 for the trigeminal (fig. 21, C, 5). 



In front of these large bones the lateral parts of the 

 cranial walls remain cartilaginous for a short distance, and 

 then there follow two elongated bones, the orbitosphenoids 

 (tig. 21, B and C, 11), pierced by the foramina for the exit 

 of the optic nerves. These bones partly correspond to the 

 sphenethmoid of the frog. 



The membrane bones connected with the cranium are the 

 parietals, frontals and prefronto-lachrymals on the dorsal 

 surface, and the parasphenoid on the ventral surface. 



The parietals (fig. 21, A and C, 6) roof over the posterior 

 part of the great dorsal fontanelle and overlap the exoccipito- 

 periotics. They meet one another along a sinuous suture in 

 the middle line, as do also the frontals which overlap them 

 in front. The frontals and parietals both extend for a short 

 distance down the sides of the cranium and meet the orbito- 

 sphenoids. The prefronto-lachrymals (fig. 21, A and C, 7) 

 connect the frontals with the maxillae. 



On the ventral surface is the large parasphenoid (fig. 21, 



