THE VERTEBRATE BODY 



133 



In most aquatic Vertebrates the trunk very gradually merges 

 into a large muscular tail: the region posterior to the coelom and 

 anus. Thus the Vertebrate tail is a unique structure — the tail 



Lung Spinal cord 



Mesonephros 



Notochord /Coelom 



Oral cavity 

 Internal gill slits I 



Heart' 



Stomach 

 Liver 



Bile duct Spleen 



Urinary duct 

 Cloaca 

 Genital duct 

 1 Urinary bladder 



Fig. 94. — Body plan of an ideal Vertebrate. Longitudinal section of female. 



of Invertebrates terminating with a segment bearing the anus. In 

 many terrestrial Vertebrates the tail has become practically an 

 inconsequential unpaired appendage. 



The Vertebrate coelom comprises two chief parts — a large ab- 

 dominal chamber and a small anterior chamber. The latter con- 



Dorsal fin 



Neural arch 

 Spinal cord 



Centrum of vertebra 



Transverse process^ 



Intermuscular rib 



Subperitoneal rib 



Ventral muscles 



Gonad 



Mesentery 



Fin ray 



Dorsal muscles 

 Dorsal aorta 



Cardinal vein 

 Mesonephros 



Intestine 

 Peritoneum- visceral layer ' 

 Fig. 95. — Body plan of an ideal Vertebrate. Transverse section. 



Mesonephric duct 

 Pronephric duct . 

 Lateral vein 

 Coelom 

 Peritoneum- parietal layer 



stitutes the pericardial chamber in Fishes but in higher forms 

 it is divided into two parts, one (pericardial) investing the heart 

 and the other (pleural) investing the lungs. The lining membrane 



