=External structure=[16] (fig. 112).--Examine the general configuration and make-up of the body. Note the deep, laterally flattened _trunk_ and paddle-like _tail_. The _head_ is closely fitted to the trunk without any neck. Note that the body is thickly covered with firm, hard _scales_, arranged like the shingles on a roof. Remove one of these scales and examine it under a hand lens. What sort of an edge has it? Such a scale is said to be _ctenoid_. The body of the sunfish terminates behind in the _caudal fin_, a series of cartilaginous rays connected by thin skin and attached to a bony plate at the end of the backbone. Along the median dorsal line will be noted another fin composed anteriorly of spines and posteriorly of soft rays jointed and branched. This is the _dorsal fin_. How many spines has it? Anterior to the caudal fin on the ventral surface is a median unpaired _anal fin_. How many spines has it? Anterior to the anal fin are the _ventral fins_, while on the sides of the body back of the head in a line with the mouth are found the _pectoral fins_. The ventral fins, attached to a rudimentary pelvis, correspond to the hind legs of the other vertebrates. The pectoral fins, attached to the shoulder girdle, correspond to the arms. In front of the anal fin note a small pit-like opening, the opening from the kidneys and reproductive organs, and just anterior to this a large aperture, the _anus_. At the anterior end of the head note the broad _mouth_, surrounded by a complicated system of bones. Note the large _eyes_ surrounded by a series of small bones, the _orbital chain_. Just anterior to the eyes are two pairs of openings, one pair of each side opening into a closed sac. What are these openings? Note the presence of various bones on the side of the head, each covered with a thin layer of skin. These are _membrane bones_, characteristic of fishes. Are there any external ears in the fish? Examine the inside of the mouth. Is there a _tongue_? If so, of what character? Are there _teeth_? If so, where are they situated? Note along each side extending to the base of the tail a line of modified scales, on each scale a little mucous tube, the whole series constituting the _lateral line_. These scales are intimately associated with a large nerve (the _vagus_), and probably serve an important part, not yet clearly understood, in the life of the fish.