496 FISHES. 



Skin. 



The small scales which cover the body are developed in 

 the dermis, and are without any bone cells. Their free 

 margin is even, a characteristic to which the term cycloid is 

 applied, in contrast to ctenoid, which describes those scales 

 which have a notched or comb-like free margin. Over the 

 scales extends a delicate partially pigmented epidermis. 



Appendages. 

 The pectoral fins are attached to the shoulder girdle just 

 behind the branchial aperture. The pelvic or ventral fins, 

 attached to what is at most a rudiment of the pelvic girdle, 

 lie below and slightly in front of the pectorals — far from the 

 normal position of hind limbs. 



Fig. 165. — External characters of a Teleostean — a carp. 

 (After Leunis.) 



Tv., Dorsal unpaired fin ; .S"., homocercal caudal fin : A., ajial fin ; 

 B.B., Pectoral and pelvic paired Irns. Note also the lateral line and 

 barbule. 



Muscular System. 



The main muscles of the body are disposed in segments, 

 — myotomes or myomeres, separated by partitions of con- 

 nective tissue. 



Skeleton. 



The Vertebral column consists of biconcave or amphi- 

 coelous bony vertebra;. Each centrum in the trunk region 

 bears superior neural processes, uniting in a neural arch 

 crowned by a neural spine, and transverse processes pro- 



