192 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Foramina of Spinal Nerves. — All the neural arches 

 except that of the atlas and usually about the last 5 are 

 perforated by two foramina on each side for the exit of the 

 spinal nerves (figs. 12, 14, 17, 18, 19). The ventral 

 foramen is usually situated a little anterior to the dorsal 

 one. Of the last 5 caudals the last is not perforated at 

 all, and the preceding 4 have only one perforation on each 

 side (fig. 19). The last vertebra, as of course in all the 

 other caudals, has both a neural and a haemal canal. 



Zygapophyses. — As shown in fig. 18, the anterior 

 zygapophyses decline after about the 14th vertebra, and 

 about the last 7 caudals have practically no zygapophyses 

 at all. After the 15th the pre-zygapophysis is much re- 

 duced, and onty very slightly overlaps the vertebra in 

 front or does not do so at all. Hence behind this vertebra 

 the post-zygapophyses are entirely lacking. 



Strengthening Ridges. — These are disposed much the 

 same as in the trunk vertebra?, except that in the hinder 

 caudals there is a tendency for the ridges to be collected 

 into one strong ridge situated mid-laterally on the 

 centrum. This, however, does not obtain in all the pos- 

 terior caudals (cp. fig. 19). 



Notochord. — All the caudals have a notochordal canal 

 except occasionally the last. The centra of the most pos- 

 terior vertebrae are always less ossified than those in front, 

 and hence the notochordal spaces are larger. The urostyle 

 is deeply excavated also, but the excavation extends 

 straight backwards and does not turn up. 



Accessory Ribs.— The tubercles which have been 

 identified as the remains of the accessory ribs are well 

 marked on the anterior caudals, but diminish backwards 

 and are practically absent on about the last 12. In the 

 anterior caudals they occupy the position of the transverse 

 processes of the trunk vertebrae. 



