47 



tliose of the trunk vertebras, 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.R.*), 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 Avitli 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.A.v.^) which lodges the large first 

 axonost of the anal fin. 



The following points of interest may be noted in the 

 caudal vertebrae. 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, and project 

 more posteriorly. Both spines aie, however, always fur- 

 rowed longitudinally for the reception of the large verti- 

 cal sheet of ligament connecting them with each other. 

 The structure of the last vertebra will be described in the 

 section on the caudal fin. 



