LIASSIC FORMATIONS. 



55 



which is single and slight ; and it includes upwards of thirty vertebra!. These vertebrae, 3 

 lines in length of centrum in the first five, progressively increase to a length of 1 inch at 

 the twelfth, begin to shorten gradually after the fifteenth, the twenty-first being 11 lines, 

 the twenty-fourth 9 lines, the twenty-eighth 6 lines, and the thirtieth 5 lines in length. In 

 breadth or thickness the vertebra) decrease from the first to the tenth ; and then again 

 gradually from the fifteenth to the last, which is filiform. 



The first caudal, or the first of the series here preserved, has the anterior articular 

 surface of the centrum subconcave. The inferior surface describes a slight concavity 

 lengthwise ; the upper part of the anterior half projects as a parapophysis, the end of 

 which has been broken off, showing the open cancellous structure. A ridge from its upper 

 part was continued to the fore part of the anchyloscd neural arch. This arch developed 

 zygapo})liyses, of which the anterior extend beyond the centrum ; but they are better 

 shown in succeeding vertebra). 



In the second caudal the base of the parapophysis has receded and now ])rojects from 

 the upper part of the side of the centrum, occupying more than its middle third. Part 

 of a quadrate spinous process is here preserved, projecting above the centrum as far as 

 the vertical diameter of that element. 



In the third caudal the base of the parapophysis, reduced in vertical thickness, 

 occupies the same positions and longitudinal extent. The postzygapophysis, after a deep 

 hind notch of the neurapophysis, curves over the prezygapophysis of the succeeding 

 vertebra, which enters that notch. 



In the fourth caudal the base of the parapophysis has lost in longitudinal as well as 

 vertical extent, and is more posterior in position. The subconvexity of the hind articu- 

 lation of the centrum is here well shown. The confluent neural arch is low, attached to 

 rather more than the fore half of the centrum. The postzygapophysis does not extend 

 back beyond the centrum ; the prezygapophysis is continued ])cyond the front or concave 

 surface of the centrum into the neural notch of the })receding vertebra. 



In the fifth caudal the parapophysis is smaller and more posterior. The neurapo- 

 physis rises from the anterior half of the side of the centrum and continues to show the 

 zygapophysis, though reduced in size. Between the fifth and sixth caudals a small, 

 slender hasmapophysis (/<) has been articulated to the under part of the intervertebral 

 space. 



The reduced parapophysis is continued from the sixth caudal ; this vertebra shows a 

 much reduced indication of neurapophysis. The base of a ha^mapophysis crosses the lower 

 part of the space or joint between it and the seventh caudal, then expands both forward 

 and backward, and more so in the latter direction ; the inferior border of this expansion 

 is straight. 



In the seventh caudal the prezygapophysis is still indicated, though nuich reduced in 

 size. The hannapophysis, siniihu- in shape to the preceding one, is longer ; and three bone- 

 tendons rise from the side of the hind projection of this haemal arch. 



