27 2 ELEMENTARY ZOOLOGY 



the spinal cord and from which projects a spine. Below, 

 the processes spread apart, surrounding the kidneys and 

 partly enclosing the air-bladder. To these processes ribs 

 are loosely attached. The caudal vertebrae have no ribs 

 and leave no room below for viscera. Their lower arch 

 (hsemal), similar to the dorsal (neural) arch, surrounds a 

 blood-vessel. The fins of a fish are composed of bony 

 rods or rays joined by membrane. Some of these rays 

 may be unbranched and unjointed, being then known as 

 spines, and usually occupy the front part of the fin. 

 Other rays are made up of little joints and are usually 

 branched toward their tip. Such ones are called soft 

 rays. Soft rays make up the greatest part of most fins. 

 The vertical fins are on the middle line of the body. 

 These are the dorsal above, anal below, and caudal form- 

 ing the end of the tail. The paired pectoral and ventral 

 fins are ranged one on each side corresponding to the 

 arms and legs of higher animals. The pectoral fin or 

 arm is fastened to a series of bones called the shoulder 

 girdle. These bones do not correspond to those in the 

 shoulder girdle of the higher animals, and the various 

 parts in the two structures are differently named. The 

 uppermost bone of the shoulder girdle is usually attached 

 to the skull. To the lowermost is attached the rudimen- 

 tary pelvis, which supports the hinder limb or ventral fin. 

 Usually the pelvis is farther back and loose in the flesh, 

 but sometimes it is placed far forward, being occasionally 

 attached at the chin. 



The head contains the various bones of the cranium, 

 usually closely wedged together and not easily distin- 

 guished. The jaws are each made of several pieces ; the 

 lower one is suspended from the skull by a chain of three 

 flat bones. The jaws may bear any one of a great variety 

 of forms of teeth or no teeth at all, and any of the bones 

 of the mouth-cavity and throat may have teeth as well. 



