552 PISCES— FISHES. 
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 vertebre 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- 
bre (Fig. 294), the centra (¢.) bear not only 
superior neural processes (7.@.), but also 
inferior heemal processes (4.a.); they are of 
course without ribs. 
Fic.294.—Cau- At the end of the vertebral column lies 
dal vertebra q fan-shaped hypural bone which helps to 
ofhaddock. support the tail, and is developed from an 
hee pee enlarged hemal arch. The fin-rays are 
et jointed flexible rods, which in the dorsal and 
. anal fins are attached to the ends of inter- 
spinous bones alternating with the neural and hzemal 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) :— 
(2) Around the foramen magnum: basi-occipital, two ex-occipitals, 
and a supra-occipital. 
(4) Along the roof: sepra-occipital, paréetals, frontals, mesethmoid, 
nasals. Beneath the parzeta/s lie the alisphenoids. 
