20 COMPARATIVE DENTAL ANATOMY 



brae. It includes the Fishes, Reptiles, Birds, and 

 Mammals. From the vertebral column the limbs 

 are suspended, and by it the vital organs are 

 held in place. It is the central structure and 

 mainstay of the framework of the body. 



A transverse section of a vertebrate body re- 

 veals two cavities or tubes, which are separated 

 by the vertebral column. The upper cavity or 

 canal, which is formed by the arches of the verte- 

 brae, contains the spinal cord and brain, and so 

 is called the neural arch or cavity. The lower 

 and larger cavity or tube is below the vertebral 

 column, is formed by the ribs and abdominal 



—3 



Fig. 1. — Section of Vertebrate, a, The neural arch; b. The visceral arch. 



walls, and contains the vital organs: the viscera. 

 Hence it is called the visceral arch or cavity. 



The nervous system of Vertebrates consists of 

 the spinal cord and the brain, which is covered 

 by the especially developed cranium. Nerve 

 branches and filaments are sent from the cerebro- 

 spinal axis to all portions of the body. Many 



