S UBPH YL UM VER TEBRA TA 



317 



In all the vertebrates below the mammals the coelom is divided into 

 a pericardial cavity containing the heart and a general body cavity. In 

 the mammals it includes a pericardial cavity, a thoracic cavity containing 



Lung 



Pancreas 



Pharynx 



Brain 



Mesonephros 

 .Notochord 



Coelom 



Mouth 



Gill 

 slits 



Cloaca 



Heart Stomach 



Urinary 

 bladder 



Oviduct 



Fig. 210. — Diagrammatic longitudinal section of the female of a lower vertebrate. {Re- 

 drawn, with modifications, from Hegner, '' College Zoology," after Wiedersheim,.) 



the lungs, and an abdominal cavity filled with the organs of the digestive, 

 excretory, and reproductive systems. 



The general arrangement of organs within the body may best be 

 understood by the aid of diagrams (Figs. 210 and 211) showing ideal 



Neural 

 arch 



Centrum 

 of \/erfebra, 



Dorsal aorta 



Cared nai 

 vein 



Mesonephric 

 c(uct 



Lateral vein 



Dorsal fin 

 Fin ray 

 Yp^^^^^::^^^^^ Spinal cord 



Inter muscular 

 rib 



Mesonephros 



Subperitoneal 

 rib 



Pronephric ducf 

 Gonad 

 Coelom 



Peritoneum 



Me.senfery Intesti ne 



Fig. 211. — Diagrammatic cross section of a lower vertebrate. {From, Parker and Haawell, 



" Text-book of Zoology.") 



longitudinal and cross sections, neither of which corresponds precisely to 

 the structure of any one vertebrate but both of which bring out general 

 relationships illustrated more or less completely in all. 



