552 



PISCES FISHES. 



net 



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. 



Muscular system. The main muscles of the body are 

 disposed in segments, myotomes or myomeres, separated 

 by partitions of connective tissue. The effective swimming 

 organ is the posterior body and the tail, as contrasted with 

 the pectoral fins in the skate. 



Skeleton. The vertebral column consists of biconcave 

 or amphiccelous bony vertebrae, and is divided into two 

 regions only, caudal and pre-caudal. The 

 spaces between the vertebrae are filled by 

 the remains of the notochord. Each cen- 

 trum in the trunk region bears superior 

 neural processes, uniting in a neural arch 

 crowned by a neural spine, and transverse 

 processes projecting from each side. Artic- 

 ulated to the distal ends of the transverse 

 processes are the downward curving ribs, 

 and also more delicate intermuscular bones 

 which curve upwards. In the caudal verte- 

 brae (Fig. 294), the centra (<r.) bear not only 

 superior neural processes (n.a.\ but also 

 inferior haemal processes (&#.); they are of 

 course without ribs. 



At the end of the vertebral column lies 

 dal vertebra a fan-shaped hypural bone which helps to 

 of haddock. SU pp 0r t the tail, and is developed from an 

 trTm! enlarged haemal arch. The fin -rays are 

 haemal jointed flexible rods, which in the dorsal and 

 anal fins are attached to the ends of inter- 

 spinous bones alternating with the neural and haemal spines, 

 and connected with them by fibrous tissue. 



The skull includes the following bones, which may be 

 grouped in the following regions (the membrane bones in 

 italics) : 



(a) Around the foramen magnum : basi-occipital, two ex-occipitals, 



and a sugra-occipital. 



(b) Along the roof : jW^nz-occipital, parietals, frontals, mesethmoid, 



nasals. Beneath the partetals lieTnTalisphenoids. 



FIG. 294. Cau- 





