276 AN INTRODUCTION TO ZOOLOGY 



facing outwards and downwards. The transverse process is short, 

 but stout, being in reality a portion of a rib fused with a true trans- 

 verse process and the combined structure is perforated by a 

 vertebrarterial canal through which the vertebral artery runs. 



The remaining cervicals are characterised by a small flattened 

 centra, only moderately developed neural spines and stout trans- 

 verse processes formed by the fusion of part of a rib with the 

 transverse process, and this combined structure is pierced by the 

 vertebrarterial canal. 



The thoracic vertebrae are readily distinguished by bearing 

 movably articulating ribs. Their neural spines are very strongly 

 developed, forming long stout flattened rods, of which the tenth is 

 approximately vertical, while those in front slope backwards and 

 those behind forwards. The centrum is short and thick, and bears 

 at the front and hinder ends a small facet which, with that of the 

 next vertebra, constitutes an articulating area for the head of 

 the rib. In the last three or four this surface lies entirely on the 

 anterior end of one centrum, and is not shared by the two. The 

 transverse processes are well developed, and have an articular 

 surface on their under face, for the tubercle of the rib : these facets 

 are lacking from the last three or four vertebrae. On the neural 

 arch of the ninth vertebra in the series a pair of slightly lateral 

 wing-like processes passing dorsally appear. These are the meta- 

 pophyses, and from the tenth onwards they are joined with the 

 prezy gapophy ses . 



The lumbar vertebrae possess stout centra ; their neural spines 

 are not so high, but are blade-like, and their metapophyses well 

 developed. The transverse processes are short flattened rods 

 projecting outwards and downwards. In addition to these other 

 processes are also developed, the hypapophyses, triangular blade- 

 like projections from the mid ventral line of the centrum, and the 

 anapophyses, small short processes running backwards from the 

 hinder end of the neural arch below the postzygapophyses but above 

 the inter vertebral notches. 



The sacral vertebrae are all fused together, but, nevertheless, 

 the lines of junction between them can be easily identified. Strictly 

 speaking, only those vertebrae articulating with the ilia, generally 

 one but at most two, can be termed the sacrum, but it is customary 

 to apply the term to the whole of the vertebrae fused with them to 

 form one mass. 



The caudal vertebrae rapidly decrease in size and complexity, 

 losing their processes, and even towards the end of the tail, their 

 neural arches, so that the terminal members of the series are repre- 

 sented only by their rod-like centra. 



