412 ZOOLOGY. 



girdle is cither lyre-shaped or forked, like a bird's wish-bone,, 

 curved forward, and with each side connected below ; the* 

 fishes in this respect differing from the Batrachians (Gill). 

 The shoulder girdle is usually closely connected by a series 

 of intervening bones with the skull, and makes its first ap- 

 pearance opposite the interval between the second and third 

 vertebras. 



The skull and skeleton may be either cartilaginous or bony, 

 and the bones of the head and skeleton very numerous. In 

 some sharks there are 365 vertebra ; in some bony fishes 200, 

 while in the Plectoynathi (fishes like the sun-fishes and Ba- 

 listes) there may be no more than fifteen ; thus in some 

 fishes there may be about one thousand separate bones. No 

 fishes have a well-defined sternum or breast-bone, this bone= 

 appearing for the first time in the Batrachians. The verte- 

 brae are almost always biconcave ; this is the simplest, most 

 primitive form of vertebra! ; it forms a weak articulation, 

 admitting, as Marsh states, of free, but limited motion. 



All fishes breathe by gills, which are supported generally 

 on four or five cartilaginous or bony supports or arches. The 

 gills are never purse-shaped, as in the lampreys, and are 

 mostly situated within the head, in front of the scapular arch. 



The mouth is generally armed with teeth varying greatly 

 in number and form, and in the bony fishes especially, not 

 only the jaws, but any bony projections, such as the palatine, 

 pterygoid and vomerine bones, as well as the tongue and pha- 

 ryngeal bones may be armed with teeth, so that the food is. 

 retained in the mouth and more or less torn and crushed be- 

 fore being swallowed. 



Fish have no salivary glands. The tongue moves only as 

 a part of the hyoid apparatus upon which it is attached. 

 After being crushed and torn in the mouth the food passes: 

 through a short throat or oesophagus into the stomach. The 

 intestine is generally provided at the anterior end with 

 several or numerous ccecal appendages which are especially 

 abundant in the cod. The gut is twisted once or twice be- 

 fore reaching the vent, but is usually much shorter than in 

 the air-breathing Vertebrates, while the vent is placed much 

 nearer the mouth than in the tailed Amphibians, thus sepa- 



