22 



VERTEBRATE ANIMALS OF THE UNITED STATES 



noids, gill-arches, tongue and pharyngeals (Fig. 9). Short, slender, 

 close-set teeth are called villiform; long, sharp teeth which project 

 beyond the level of the others are called canine; teeth with blunt tips 

 used for crushing shells are called molar; flat, mosaic-like teeth are called 

 paved or tessellated; front teeth with cutting edges are called incisot'. 



Internal Structures. — A knowledge of the internal anatomy of a 

 fish is usually not necessary in order to make a systematic description 



Fig. 9. — The inside of the mouth (of the rock bass, Amhlopliles rupestris) showing the 

 dentition and the gill-arches: a, the roof of the mouth; b, the floor of the mouth: dn, dentary; 

 ecp, ectopterygoid; enp, entopterygoid; hy, hyoid; Iph, lower pharyngeal arch; pi, palatine; 

 pmx, premaxillary ; hi, tongue; iiph, upper pharyngeal arch; vo, vomer {from Fishes of 

 Illinois) . 



of it. The following features, however, are occasionally referred to 

 in the descriptions in this book: the shape of the stomach; the number 

 and character of the pyloric appendages or caeca of the stomach; the 

 length and character of the intestine; the presence or absence of the air 

 bladder, and its character when present; the character of the four ante- 

 rior vertebrae, whether they are coossified and have some of their ele- 

 ments detached to form the Weberian ossicles which connect the air 

 bladder with the ear; the unossified portion of the top of the skull in 

 certain fishes known as the fontanelle. 



History.^ — Fishes, conspicuous and abundant animals as they 

 are and important in the dietary of all peoples, have attracted the 

 interest of naturalists from time immemorial. The modern scientific 



