10 



MAEINE EEPTILES OF THE OXEOED CLAY. 



which is concave, the anterior convex) for union wiih corresponding facets on the 

 upper surface of the stapes. In both elements these facets are separated by a deep 

 groove (g.), so that when the two bones are in apposition a channel is enclosed 



Text-fig. 3. 



Prootic, opisthotic, and stapes of OpJiiltahnosaiints : A, inner face of prootic; 33, outer face of prootic ; 

 C, right stapes from above ; D, ditto from front ; E, right opisthotic from below ; F, ditto from above. 

 (A, B, E. 2161 ; C-P, E. 2162 : all | nat. size.) 



hoc./., facet for basioecipital ; exo.f., facet for esoccipital ; g., grooves in stapes and opisthotic, forming a 

 foramen when the two are articulated with one another ; h.c, channel for horizontal semicircular 

 canal; op./., op./'., the two facets on the stapes for the opisthotic; ^.v.c, channel for posterior 

 vertical semicircular canal ; q.f., facet for quadrate ; r., ridge on shaft of stapes ; sq.f., facet for 

 squamosal; st.f ., st.f ., the t«o facets of the opisthotic for the stapes; t., tuberosities on shaft of 

 opisthotic. 



between them, running from within outwards and probably transmittmg one of 

 the nerves (Ithe ninth) issuing from the jugular foramen. Above the posterior of 

 the two facets just referred to, there is a large, roughly semicircular surface (boc.f.), 

 by which the bone unites with the basioecipital. Above this again, and separated 



