474 



TELEOSTEI 



Order I. Teleostei. 



[CH. 



"We shall begin the study of Osteichthyes with the study of the 

 order which includes the vast majority of living fish, viz. Teleostei. 

 The word means the completion or perfection of bone (Gr. re'A.09, end, 

 ooreov, bone), and on the whole it is justified as a description of 

 these fish. Teleostei are above all characterised by the structure of 

 the skull and vertebral columns. In these the cartilage is largely 

 replaced by bone developed from the modification of the connective 



FIG. 232. Illustrating the mode of formation of the vertebral column in 



Teleostei. 

 A. Early stage in development. B. Later stage in development. The 



circles indicate the gelatinous tissue of the notochord, dots indicate 



cartilage, and close parallel lines bone. The oblique parallel lines indicate 



the boundaries of successive myotomes. 

 1. Basidorsal with neural arch. 2. Notochord. 3. Basiventral with 



haemal arch. 4. Bony ring connecting basidorsal and basiventral 



pieces and forming the centrum. 



tissue around it but which eats into and replaces the cartilage, and 

 is termed cartilage bone. 



The vertebral column is composed of hour glass shaped or nearly 

 cylindrical centra hollow at both ends, resembling in shape the 

 centra of Elasmobranchii and like them denominated Amphi- 

 coelous (Gr. a/A^t, both, KOIA.OS, hollow), but of course composed of 

 bone. Between two adjacent centra the notochord persists through- 

 out life; in the young Teleostean it is continuous throughout the 

 length of the fish but in the adult it usually becomes completely 

 obliterated in the centre of each centrum. With each centrum 



