MR. W. H. FLOWER OX THE OSTEOLOGY OF THE SPERJI-AVHALE. 345 



series almost equalling the hinder ones in importance. On the thirteenth vertebra arti- 

 cular facets are faintly indicated on the anterior edge only. 



Having now examined the modifications of the different parts of the caudal vertebras, 

 their bodies, neural arches, transverse processes, arterial foramina, and articular facets 

 for lisemapophyses, a few words must be said on the peculiarities of the different vertebrae 

 of the hinder part of the series taken as a whole. 



The first twelve, or chevron-bone-bearing vertebrae, present a gradual and steady 

 change in size and general character from first to last, this change consisting of the 

 gradual reduction in size of the centrum, reduction of the neurapophysis, and reduction, 

 to absolute disappearance, of the transverse processes. In the thirteenth caudal vertebra, 

 a great change takes place in the size of the body, though the same general form is 

 maintained. The anterior and posterior surfaces are nearly subcircular ; but the absence 

 of any transverse processes, and the presence of a roughened low tuberosity representing 

 the neurapophysis, and of the inferior tuberosities for the attachment of the htemapo- 

 physes, make the whole bone higher than broad. The most remarkable feature about 

 this vertebra is the rapid manner in which it diminishes posteriorly, the posterior sur- 

 face for the attachment of the intervertebral substance being 2" less in diameter than 

 the anterior. 



Fig. 11. 



Twelfth iind seventeenth caudal vertebroe. 



The succeeding vertebra is of very simple character, being reduced to a centrum with 

 a slight tubercle covering the neural canal to represent the spinous process ; in conse- 

 quence of this, the whole bone is still slightly higher than broad. After this a sudden 

 change in form takes place ; in the fifteenth and all the succeeding vertebrae the breadth 

 predominates over the height. The fifteenth to the twentieth inclusive present very 

 uniform characters. They may be described generally as transversely elongated oblono- 

 bodies, flattened before and behind, above and below, and at each side. The ujiper 

 and under surfaces are remarkably alike, so much so that it requires close attention to 

 very minute characters to be able to distinguish them. The upper surface shows on 

 each side, about midway between the median line and the outer edge of the bone, the 

 funnel-shaped opening of the large circular arterial canal, which perforates the vertebra 

 nearly vertically. The quadrangular space between these perforations bears at each 

 corner four tuberosities, an anterior and a posterior pair, remnants of the neurapophysis. 



