HOLOSTE1 



327 



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. 



Fici. 305. 



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

 C, transverse section of a trunk vertebra, do, basioccipital ; 1n\ basiventral ; c, centrum ; ep, 

 epipleural ; epo, epiotic ; wo, exoccipital ; /.), foramen magnum ; li, longitudinal ligament ; my, 

 myotome ; n.c, neural canal ; n.s, neural spino ; 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 the Actinopterygii we have hitherto 



in a certain region. 



