FROM THE KIMMEKIBGE CLi.T. 435 



forms a wide depression behind the hypophysial pit Throughout this 

 extent, 38-5 millims., the j3.oor of the skull-chamber consists of a 

 continuous unbroken piece, basioccipital, which ends taperingly in 

 the depression behind the sella turcica, where the basisphenoid 

 comes into view. Thus the basioccipital overlaps the basisphenoid 

 on the upper as also at the under surface of the basis cranii. 



Laterally the persistence of the sutures and the foramina of exit 

 for the cranial nerves makes it possible to recognize in sequence 

 from behind forwards (1) a stout exoccipital, articulating with the 

 basioccipital by a broad serrated suture, and perforated at 10 millims. 

 from the foramen magnum by an aperture (for 9th nerve?). At 

 6 millims. in front of this opening is another groove (for trans- 

 mission ofTagus?), which appears to pass out between the ex- 

 occipital and opisthotic elements. This, again, is followed by a very 

 conspicuous groove, situated where the basioccipital attains its 

 greatest breadth in the floor of the skull-chamber. In front of 

 this, where the prootic might be expected, is the upper opening of 

 a deep funnel-like pit, which descends within the bone into the 

 basisphenoidal process visible at the under surface of the skull. The 

 form of this pit does not suggest the transmission of blood-vessel or 

 nerve, whilst its situation hints that it may be part of the auditory 

 apparatus, possibly an air-channel connected with the middle ear. 

 The fact that in old Iguanodons the inferior basisphenoidal pro- 

 cesses are hollow sinuses * favours this conjecture. A wide groove, 

 presumably for the 3rd nerve, separates the prootic and ali- 

 sphenoid. 



PL XYIII. fig. 5. Another fragment (I. 9) comprises the back of 

 the skull and the sides nearly to the extent of the piece just described. 

 The supraoccipital bone contributes the upper boundary of the 

 foramen magnum, as in extant lizards. It is not excluded from this 

 opening as in crocodiles — a point worthy of notice, because the general 

 form of the occiput, so far as it can be recognized in this fossil, has a 

 crocodilian likeness, as has also the occiput in my Brooke Iguanodon- 

 skuU. Immediately above the foramen magnum the supraoccipital 

 stretches laterally outwards to what are apparently the roots of a 

 stout suspensorium (for the attachment of the quadrate bone), now 

 broken off and missing. This is a strong pyramidal projection, 

 below constructed of the blended exoccipital and opisthotic, above 

 of another and distinct part, parietal. Between these two parts of 

 the suspensorium the broken surfaces show that an extreme lateral 

 extension of the supraoccipital intrudes. Nearly at its mid- 

 height this bone abruptly contracts to less than half its breadth 

 below (22*5 millims), being here encroached on and overlapped by 

 the suspensorial extension of the parietal. This narrowing of the 

 supraoccipital is too symmetrical to be altogether due to the down- 

 ward crushing of the parietal upon it; it has doubtless been in- 

 creased by this, but is a natural conformation. The upper border 

 of the supraoccipital is a smooth edge, which was connected with 



* I learned this many years ago in a fragment of a very large old skull 

 in Ihe collection of the Rev. W. Fox. 



2g2 



