156 MARIXE REPTILES OF THE OXFORD CLAY. 



The exoccipitals (ea\o.) are large and complicated bones. They meet above the 

 foramen magnum, from which they thus exclude the supraoccipital. Below they unite 

 with the basioccipital, forming a small part of the rim of the occipital condyle and the 

 outer face of the downwardly directed lateral processes. External to these there is a 

 notch from which a short groove runs upwards and inwards, terminating in the large 

 carotid foramen, which is thus more on the hinder face of the bone than in Steneo- 

 saurus; it is probable that this foramen also transmitted the vagus group of nerves. 

 External to the notch the lateral wing of the exoccipital unites closely with the 

 hinder face of the quadrate. Above this is a deep groove passing at its outer end 

 into a foramen and marking oft the prominent paroccipital ridge, the upper edge of 

 which joins the parietal and squamosal, forming the hinder face of the post-temporal 

 bar. The outer end of the paroccipital bar is very prominent and terminates in a 

 roughened surface. 



The supraoccipital (s.oc.) is a small bone, which, as above noted, is completely 

 excluded from the foramen magnum by the exoccipitals. Its suture with the parietals 

 is nearly straight and is interrupted at its outer ends by a pair of foramina which run 

 in between the two bones. From these openings the lateral sutures with the 

 exoccipitals run downwards and inwards to the short and nearly straight inferior 

 border of the bone. 



The foramina in the occipital region are probably as follows: — (1) the carotid 

 opening referred to above, through which the vagus group of nerves probably also 

 passed (PI. XIII. fig. 3, car. & X?) ; (2) a small opening near the lower part of the 

 border of the foramen magnum, presumably for the hypoglossal (XII) nerve; (3) a 

 large foramen at the bottom of the groove separating the paroccipital process of the 

 exoccipital from the part uniting with the quadrate, probably for the facial (VII) 

 nerve — its anterior edge may be formed by the quadrate. There are also two or 

 three small openings in the exoccipital external to, but about on the same level with, 

 the hypoglossal opening, but their nature is unknown. 



The basisphenoid (is., text-fig. 58) unites posteriorly with the basioccipital ; on the 

 ventral surface its posterior border forms a thin sharp ridge constituting the anterior 

 wall of the fossa, at the bottom of which is the median eustachian opening. Laterally 

 it unites with the anterior face of the ventro-lateral processes of the basioccipital. In 

 the mid-ventral line there is a strong cristiform ridge, upon the anterior end of which 

 converge two curved ridges which mark the line of union with the posterior ends of the 

 pterygoids. These bones unite with one another beneath the basisphenoid for some 

 distance, but seem to have been separated in front by the posterior end of the vomer 

 (parasphenoid), which unites with the anterior portion of the ventral face of the basi- 

 sphenoid, and this bone terminates abruptly in front in a vertical surface. 



The sclerotic plates, which are known to have been present in members of this 

 family, are very larely found, cnly two or three plates, belonging to two individuals, 



