METKIOKHYNCHUS. 155 



terminates abruptly in front. The whole form and relations of this bone seem to 

 show that it is actually the parasphenoid (vomer of Broom), while the paired elements 

 usually called vomers in reptiles (pve-vomers of Broom) are either absent or small. 



The pterygoids (pt., text-fig. 58) are usually greatly crushed, so that their relations 

 to the surrounding bones are rarely clear. Posteriorly they unite in the middle line 

 beneath the basisphenoid (and I parasphenoid), their posterior border forming a curved 

 ridge which runs up on the side of the basis cranii to the point at the base of the 

 lateral processes of the basioccipital where they join the downward processes of the 

 exoccipitals. Laterally this posterior portion of the pterygoid seems to be overlapped 

 by the inner prolongation of the quadrate, which extends inwards nearly to the middle 

 line. In front of their median union the pterygoids are separated in the middle line 

 by the vomer (parasphenoid), which, as above noted, forms a median ridge along 

 the concave roof of the nasal fossa. In the region of this fossa the bones widen out 

 considerably, and their ventral surfaces form shallow concave pterygoid fossa? ; their 

 outer border is convex with two or three tooth-like projections directed forwards, 

 while towards the hinder end of this border there is a surface for a squamous suture 

 with the transpalatine (t.p.), which seems to have been very small, but in no case is 

 preserved. In front of the level of the ventral border of the internal narial openings 

 the pterygoids run off into thin triangular processes, which overlap the vomer and 

 the palatines, forming the roof to the posterior part of the nasal canals (text-fig. 59, 4). 

 Anteriorly they terminate in points at about the level of the middle of the suborbital 

 vacuity. 



In its general form the occipital surface (PI. XIII. fig. 3) in the uncrushed skull is a 

 triangle, of which the base (width between the outer angles of the quadrates) is 

 rather more than twice the height (from lower border of the occipital condyle to the 

 summit of the parietal crest) ; but in nearly all cases the crushing undergone has 

 completely destroyed this form, the foramen magnum, as a rule, being almost com- 

 pletely obliterated. 



The basioccipital {hoc.) forms the whole of the occipital condyle, except a small 

 portion of the upper outer border, which is borne on the exoccipitals. The upper 

 surface of the condyle between the exoccipitals is fiat or gently concave, but the 

 remainder is nearly evenly rounded, its transverse diameter being slightly longer than 

 the vertical ; there is a pit in the middle of the convexity. Ventrally the condyle 

 is sharply delimited by a short neck. In front of this the sides of the bone are 

 produced downwards and outwards into the large lateral tuberosities which are 

 separated by a deep fossa, at the anterior end of which is the median eustachian 

 opening (eu.tn.). This is bounded in front by the hinder edge of the basisphenoid (is.), 

 which no doubt it penetrated. The outer sides of the lateral tuberosities are formed 

 by a thin downwardly directed process of the exoccipitals ; their extremities are 

 much roughened. 



x'2 



