47 
those of the trunk vertebra, is deeper than the anterior, 
and hence the notochordal canal is thrown further for- 
wards. ‘The centrum is markedly asymmetrical, being 
larger on the eyeless side. The projection at the side of 
the centrum which possibly represents the remains of the 
accessory rib and its basal tubercle (A./?.*), with which it 
is serially homologous and to its present position on the 
centrum it has been gradually ascending from the trans- 
verse process, is larger and has a more ventral inclination 
on the ocular than on the eyeless side. Below the centrum 
are situated the haemal arch with its canal and the haemal 
spine. The latter is a thin curved laminate bone with the 
concavity directed forwards, and strengthened behind by 
two thin longitudinal ridges. In front it bears a wide 
longitudinal recess (Rec. Av.') which lodges the large first 
axonost of the anal fin. 
The following points of interest may be noted in the 
caudal vertebra. Behind the fourteenth or first caudal 
vertebra the vertebral column has a much more uniform 
structure, except that the first few caudals represent inter- 
mediate stages between the characters of the 14th and 
those of a typical caudal vertebra (cp. figs. 18 and 19). 
The asymmetry extends right down to the extremity of 
the column, but is only very slightly developed in the last 
few caudals and in the epurals and hypurals of the caudal 
fin. 
Neural and Haemal Spines.—As we pass back the 
spines get more’simple in structure, shorter, und project 
more posteriorly. Both spines are, however, always fur- 
rowed longitudinally for the reception of the large verti- 
cal sheet of igament connecting them with each other. 
The structure of the last vertebra will be described in the 
section on the caudal fin. 
