HO LOS TE 7 



3 2 7 



occipital is derived from neither of these sources, but is a new 

 ossification. 



The intestinal spiral valve is already much reduced in Amia and 

 Lepidosteus ; in the Teleostei it usually disappears altogether. 



Fig. 305. 

 Salmo salar, L. (After Bruch.) A, skull from behind. B, transverse section of the trunk. 

 0, transverse section of a trunk vertebra, bo, basioccipital ; bv, basiventral ; c, centrum ; ep, 

 epipleural ; epo, epiotic ; exo, exoccipital ; f.m, foramen magnum ; li, longitudinal ligament ; my, 

 myotome ; n.r, neural canal ; n.s, neural spine ; op, opisthotic ; pa, parasphenoid below the 

 myodome ; p.r, pleural rib ; pto, pterotic ; r, rib ; so, supraoccipital. 



Order 1. AMIOIDEI. 



The three sub-orders of the Holostei differ in the structure of 

 the vertebral column. In the Amioidei the notochord is sharply 

 constricted by well-formed centra in the only living species, Amia 

 calm, but in the earlier, more primitive forms it appears to have 

 persisted to a much greater extent. The Amioidei are distinguished 

 by the presence of separate pleuro- and hypocentra, at all events 

 in a certain region. In the Actinopterygii we have hitherto 



