286 BRITISH FOSSIL REPTILES. 



vertebra, which consist of short plcurapoph3'scs, pi i, have been advanced, hke the 

 neural arch, to the interspace between the first sacral and last lumbar vertebrae, and 

 have coalesced with both ; the major part of the expanded head of the short and strong 

 sacral rib being fixed to the sides of the expanded anterior end of its own centrum : after 

 becoming slightly constricted, the ribs expands, like the overlapping cervical ribs in the 

 crocodile, in the direction of the axis of the body, but the sacral ribs more firmly unite 

 their portion of the vertebral coluinn together by becoming confluent at their expanded 

 extremities. Al.most the whole upper surface of the sliort sacral rib has coalesced with 

 a strong, vertically developed, antero-posteriorly compressed, diapophysis, d \, PI. 9. 

 These processes are continued outwards from the whole side of the neural arch, and 

 form a series of strong transverse ridges, a l — d .5, PI. 9, progressively increasing in 

 length to the fourth, rf4 ; the fifth, rf 5, being of nearly the same length as the fourth. 

 The neurapophyses extend forwards and backwards beyond the base of the diapophyses, 

 and coalesce with each other and with the centrums, so as to convert the interneural 

 outlets for the nerves into foramina. The neural spines, probably short in comparison 

 with those in the dorsal region, and apparently more or less blended together to form a 

 continuous ridge, have been broken or worn away to their bases, which are indicated by 

 the letters « i— /; 5, in PI. 9. The bodies of the second, « 2, PI. 8, and third, s 3, 

 sacral vertebrae are compressed, and continue to present the carinate inferior surface ; 

 that of the fourth sacral s 4, and fifth sacral s 5, progressively expand, and are convex 

 beneath. In the first to the fourth sacral, inclusive, the sides of the centrum present 

 a rounded depression a little behind their middle, the neural arches of the second, 

 third, and fourth sacral vertebrae rest two thirds upon their own centrum and one 

 third upon that in advance, dipping wedgewise into the interspaces of the centrums as 

 they cross from one to another : the neural arch of the fifth sacral, like that of the first, 

 rests in a larger proportion upon its own centrum, above which its piers meet, leaving 

 a triangular neural surface before and behind their junction. The posterior articular 

 surface of the body of the last sacral vertebra is shown in PI. 11, fig. 2, ^j; it is 

 slightly concave ; the upper surface of the centrum above this end, and for about one- 

 fifth of its length, PI. 10, fig. 2, « 5, is free, the neural arch of the first caudal vertebra 

 having resumed its normal position in regard to its centrum. The posterior zyg- 

 apophyses, z' z', PI. 9 and PI. 11, are in part preserved in the last sacral vertebra; 

 the degree of diminution of the neural canal, as it extends, with partial expansions, 

 through the sacral series, may be seen by comparing fig. 1 with fig. 2, in PI. 11. 

 The coalescence of the pleurapophyses and diapophyses circumscribes a series of four 

 progressively expanding vertical canals on each side of the sacrum, the lower outlets of 

 which are shown in PI. 8, and the upper ones, o, o, o, o, in PI. 9 : the nervous 

 foramina, in the interspaces of the neural arches, open into these canals. There has 

 been a tendency to ossification in the fascia extended between the upper borders of the 

 strong boundaries of these foramina, of which the evidence remains, at/ Pis. 8 and 9, 



