MUSCULAE SYSTEM. 205 



the head and scapular arch to the base of the caudal fin. This mass 

 of muscle is not, however, so simple as it appears, but divided into 

 numerous parts. We may distinguish an upper layer where the 

 tendinous strips are directed obliquely backward, and then a second 

 and third, the last of which is situated beneath the lateral line. 

 The tendinous transverse strips here alter their direction, but cor- 

 respond to the number of vertebrae. These layers of muscle arise 

 from the skull itself, from the occipital and mastoid bones, in which 

 situation they correspond to the nuchal muscles ; also from the sca- 

 pula and clavicle, then from the lingual bone, the vertebrae and their 

 spinous processes, clothe the ribs, and are inserted by short tendons 

 into the base of the caudal fin. Below them lies another layer upon 

 the belly, which corresponds to the abdominal muscles, while the 

 upper layers are analogous to the dorsal muscles of the higher 

 animals, especially the m. m. spinalis, scmispinalis, multifidus spintB, 

 longissimus dorsi, and sacro-lumbaris. The symmetry displayed by 

 the dorsal and ventral portions of the lateral muscles, upon a perpen- 

 dicular section, is most striking, and we are in this way best enabled 

 to see the peculiar infundibuliform arrangement of the several mus- 

 cular layers. 



Each lateral muscle bends the body toward its own side, at the 

 same time producing powerful lateral inflexions of the rudder-like tail ; 

 movements so necessary in the act of swimming. The head can be 

 also moved to a slight degree, when its freedom of attachment to the 

 vertebral column admits of it. By the co-operation of the two lateral 

 muscles upon either side at their anterior part, the compression of the 

 swimming-bladder may be also affected. 



The several orders and genera of Fish naturally exhibit numerous 

 muscular varieties. Beneath the lateral muscles, between the ribs, 

 are found the intercostal muscles. In the interspaces between the two 

 great lateral muscles, both upon the dorsal and ventral side, but chiefly 

 upon the latter, two very slender muscular strips may be seen to pass, 

 as in the Perca fluviatilis, and to be interrupted only by the dorsal 

 and anal fins. 



The caudal Jin is moved chiefly by small thin muscles, which form 

 two layers, a superficial and a deep, and are inserted, like those of 

 the dorsal fins, into the rays composing it ; occasionally there occurs, 

 as in Perca, a third layer. The several rays of the caudal fin can be 

 moved by means of these upward, downward, and laterally. 



The muscles of the anterior extremities consist of two principal 

 layers, upon each of the two surfaces of the antebrachial and carpal 



