FEOM THE LOWER LIAS OF CHARMOETH. 



449 



spine is broader at the distal end than in the preceding vertebrae. 

 The anterior margin is short and straight, sloping backwards ; 

 the upper margin curved, rising obliquely backwards ; the posterior 

 margin is sigmoid, convex backwards above, and concave below, 

 nearly vertical. In the thirty-second (xxxii) the outline is much 

 simpler : both anterior and posterior margins are straight, not quite 

 parallel with each other, since they are further apart below than 

 above ; the upper margin is an elliptical curve, through which the 

 anterior and posterior margins pass into each other. The base of 

 the anterior part of the spine between the anterior zygapophyses is 

 much compressed ; it broadens out immediately behind the origin of 

 the anterior zygapophyses, and also over the posterior zygapophyses. 

 The costal pits increase in size ; but neither they nor the ribs show 

 much sign of other change down to the twenty-sixth (xxvi) ver- 

 tebra, when, however, preparations for change become evident. 



In the twenty-sixth, the rib being displaced allows the costal pits 

 to be seen ; they are now quite separate oval depressions, 0*95 inch 

 long and 0*9 inch distant from the anterior edge of the centrum, with 

 which they are connected by a ridge which continues the anterior 

 margin of each forwards. 



In the twenty- seventh (xxvn) all trace of rugosity has disap- 

 peared from the surface of the centrum, and it is now quite smooth ; 

 this continues to be the case throughout the rest of the vertebral 

 column. The neuro-central suture is marked by a swelling ridge, 

 particularly prominent in the central part of its course. 



In the twenty-ninth (xxix) the thickening of the lower end of 

 the neural arch becomes more marked, and the margin of the costal 

 pits is somewhat elevated. 



In the thirtieth (xxx) faint signs appear of a ridge proceeding 

 from the swollen end of the neural arch to the upper margin of the 

 costal pit ; in the thirty-first (xxxi) this and the ridge connecting 

 the anterior margin of the costal pit with the anterior edge of the 

 centrum have both become more marked. In the thirty-second and 

 thirty-third (xxxn and xxxiii) the costal pits begin to rise higher 

 on the centrum, and become more posterior ; the upper edge of the 

 pit swells into a marked ridge, and is connected by the previously 

 mentioned ridge, which (now become very prominent) ascends from 

 it to the swollen end of the neural arch. 



In the thirty-fourth (xxxiv) the lower costal pit has almost dis- 

 appeared, and the upper and anterior margins of the remaining pit 

 are swollen into a strong crescentic ridge, which is joined in the 

 middle by the ridge descending from the neuro-central suture. 



In the thirty-fifth (xxxv) the thickened lower end of the neural 

 arch and the ridge arising from the anterior margin of the costal 

 pit form together a single vertically descending median ridge, which 

 extends more than halfway down the side of the centrum. That 

 part of the ridge contributed by the neural arch is more swollen 

 than the other, and curves forwards as it descends, joining at an 

 obtuse angle the part contributed by the centrum, which is sigmoid 

 in outline ; the general form of the united ridge is much like that 



