40 



Branchial Arch lY. — The ceiato-branchial is less 

 strong on this side, but on the other hand the epi- 

 branchial is larger. The eerato-branchial does not articu- 

 late with the fourth basi-branchial but with the corre- 

 sponding segment of the ociilar side. 



The Superior and Inferior Pharyngeals. — The asym- 

 metry in the number of the teeth is so strongly marked in 

 the mouth, where the ocular side is practically devoid of 

 them, that it is interesting to enquire whether its effect 

 has been felt as far back as the pharyngeal bones. In 

 the inferior pharyngeal the two sides are practically the 

 same, except that in the specimen described the ocular 

 bone bore two less teeth. The left superior pharyngeal, 

 however, was appreciably the larger, and although it only 

 possessed an advantage of one in the number of teeth, the 

 teeth themselves were larger and capable of doing more 

 work. This is doubtless due to the fact that in an animal 

 lying on its left side, its food, even in the pharynx, 

 naturally gravitates to the latter side. 



7. — Yertebeal Column.* 

 (Figs. 10, 11, 12, 13, 14, 17, 18, 19). 



The vertebral column of the Plaice may be divided 

 into a trunk and tail region only, distinguished in the 

 former by the presence of ribs and in the latter by the 

 haemal canal. Although the number of vertebrae in the 

 column is subject to variation, it usually happens that the 

 first caudal vertebra is the fourteenth. 



Each vertebra is markedly amphicoelous, the anterior 

 and posterior faces being considerably scooped out in the 



* The structure and development of the vertebral column of 

 Teleostean fishes has recently been studied by S. Ussow (Bull. Soc. Imp. 

 Nat., Moscou, 1900, p. 175). Also previously in Amia and other fishes, by 

 O. P. Hay (Field Columbian Museum, Zool. Ser., vol. i., No. 1, 1895). 



