308 BIOLOGY. 



constituting what are called cesophageal maxillae. The 

 branchial organs are fundamentally also none other than 

 cesophageal rings. The lingual and palatal bones, with 

 the intermaxillary bones, belong also to the same category. 



2090. The vascular bones are displayed in the hearts 

 of many animals. The three last divisions may be 

 called visceral or splanchnic bones ; and then we have 

 tegument ary, splanchnic, and nerve-bones. 



b. Animal Osseous System. 



2091. The animal or nervo-osseous system must 

 separate from the vegetative system of bones, and be 

 placed upon the side exposed to the light. The side of 

 the inferior animal that is exposed to the light, or 

 averted from the earth, is the upper surface, dorsal region 

 or back. 



2092. The back holds the same relation to the ventral 

 side as light does to the darkness, as sun to the earth ; 

 therefore the dorsal side is of a dark, the ventral of a 

 faint or pale colour. 



2093. Back and belly are related polarwise to each 

 other. 



2094. Through the medium of the bones the dis- 

 tinction between back and belly has been definitely 

 established in the animal, and, as a consequence thereof, 

 the distinction also of right from left. Before a forma- 

 tion of bone exists, the animal is for the most part a 



\ round cylinder. 



2095. The osseous system can in itself be only sym- 

 metrically constructed. 



2096. The osseous is the only symmetrical system in 

 1 an animal. The other organs are so only in so far as 



they follow the arrangement of the osseous system. 



2097. The animal osseous system is, from its being a 

 repetition of the intestinal canal, a tube. This tube is 

 surrounded, like the trachea, by rings, between which 

 the tegumentary tube suffers constrictions. 



2098. The back is a series of numerous bony rings. 



2099. These bony rings are the bodies of the vertebrae. 



