MDRiENOSAUEUS. 



79 



laterally the body of the bone bears a pair of stout processes which project outwards 

 and downwards, their ends being truncated by large oval facets {pt.f.) which look 

 outwards and forwards and articulate with the pterygoids, which in these animals 

 extend very far back, their posterior ends, by which they unite Avith the quadrates, beiiicr 

 actually behind the occipital condyle. Between these processes the ventral surface 

 of the bone is concave from side to side ; in front of this it is flattened and greatly 

 roughened up to its anterior edge. In some cases the posterior surface of the 

 lateral processes bears a roughened surface for the attachment of muscles. 



Text-fig. 43. 



Basioccipital of Mmxenosaurus durobrivensis : A, from below ; B, from above ; 

 C, from front. (E. 2361, nat. size.) 



hs.f., facet for basisphenoiJ ; erco.f., facet for exoecipita) ; n.c, floor of Deural canal ; 

 oc.c, occipi'-al cond'yle; p'-/-i facet for pterygoid. 



The lasisjj/ienoid (b.s., PI. III. figs. 1,1 a; text-fig. 44) consists of a posterior cuboid 

 mass of bone, the antero-ventral portion of which is prolonged forwards to form 

 the floor of the pituitary fossa. The posterior face is nearly flat and fitted closely 

 against the corresponding surface of the basioccipital. In most cases the two 

 bones can be seen to make a very obtuse angle wnth one another, the axis of 

 the basis cranii in front of the basioccipital being bent a little upwards. The nearly 

 flat upper surface consists of two flattened areas united in front, but separated 

 posteriorly by a V-shaped concavity ; in life these areas were perhaps covered wiih 



