LIASSIC PLESIOSAURS. 29 



Lacertilia, to which ' neurapophysial ' ridges (Tab. XIII, fig. 2, n, n) may have been 

 attached tlie neurapophyses, but retaining, as in these Lacertilia, more or less of their 

 primitive histological fibro-cartilaginous condition. The under and lateral parts of 

 the mesencephalic centrum, called ' basisphenoid,' are covered by the largely developed 

 'pterygoids' (ib., fig. 1, 24), — the diverging appendages of a more advanced cranial 

 segment. The back part of the third or ' prosencephalic' centrum has coalesced 

 with the second, the boundary-line being indicated by a shallow depression, which 

 may have lodged the vascular appendage of the brain called ' hypophysis,' or 

 ' pituitary gland.' The sides of this part of the centrum rise, neurapophysially, 

 and terminate with a fractured and worn surface, and the rest of the centrum, 

 answering to the cetacean 'presphenoid' (9), has been broken away. Beneath 

 the fractured end of the presphenoid is the nasal ' meatus/ or canal (ib., fig. 1, r), 

 which is divided below by the junction of the palatines (ib., fig. 2, 20, 20) with the 

 pterygoids (ib., 2A, 24), so as to open upon the roof of the mouth by a pair of posterior 

 or palatal nostrils ' palatonares' (ib., r,r)- These are of a narrow, elliptical form, with 

 the long axis longitudinal, but slightly, inclined ' mesiad,' or converging anteriorly, 

 pointed behind, 1 inch 6 lines in long diameter, 7 lines across their widest part, and 

 separated anteriorly by a tract of bone 9 lines across; from the posterior end of the 

 ' palatonares' to the same part of the basi-occipital tuberosity is I inch 5 lines. The 

 palatines (ib., fig. 2, 20, 20), where they give attachment to the pterygoids, are narrow, 

 rather thick, with a shallow median channel, bounded by low, lateral, obtuse risings ; 

 external to these the palatines form the anterior ends of the ' palatonares,' and thence 

 expanding, and flattening as they stretch forwards, they unite laterally with the 

 ectopterygoids (25, 25). The pterygoids (24, 24), which form the inner and posterior 

 boundaries of the palatonares, expand as they pass backward, become thinner and 

 flatter, and retain a sutural union along the mesial line until they reach the precondy- 

 loid fossa of the basi-occipital ; underlying and concealing from view, inferiorly, the 

 basi-presphcnoid and major part of the basi-occipital. These ' basilar' plates are 

 slightly concave from side to side, and are divided from the ' tympanic ' pro- 

 cesses (24', 24') by a rising of bone, hardly to be called a ridge ; this is chiefly formed 

 by the concavity or sinking of the surface at the commencement of the under part of 

 the ' tympanic' process, which also gradually contracts in breadth as it extends 

 backward and outward to abut against the tympanic pedicle (28), which is wedged at 

 its upper or cranial half between the pterygoid (24) and par-occipital (3). 



The ectopterygoid (ib., fig. 2,25) articulates with the pterygoid near the posterior part 

 of the palatal nostril, where it is about seven lines in breadth ; this joint has been put 

 out by pressure on the right side and the ectopterygoid dislocated downward ; the 

 corresponding part is broken ofi^ on the left side, where it overlaps the pterygoid, 

 forming the outer boundary of the palatal nostril. The ectopterygoid expands as it 

 advances forward ; curving, mesially, round the fore part of the nostril to join the 



