424 



CHORD AT A. 



cavity of the myotome) early disappears and the ventral 

 element alone persists as a continuous perivisceral cavity. 



Fig. 306. — Diagrammatic Transverse Section through a 

 LATER Vertebrate Embryo. 



(Mainly after Van Wijhe.) 

 Nerve Cord. 



Meson ephric 



Tubules. 



Pronephric Duct. 



Myocoele. 

 Myotome. 



Intestine. 

 Perivisceral Coelom. 



I^ig- 307- — The Parts of the Ccelom in the Thoracic 

 Cavity of a Mammal. 



Lung. 



(After WiEDERSHEIM.) 



Vertel)ra. 



Trachea. 



^j^C^ 



Somatic Layer 



of Pleura. 

 Visceral Layer 

 V of Pleura. 



\ 

 Lung. 



I Heart. 



Somatic Layer Visceral Layer Somatic Layer Visceral Layer 

 of Pleura. of Pleura. of Pericardium, of Pericardium. 



A, The lungs. B, Cross-section of the thorax. 



In the cavity lie the heart and all the alimentary organs. 

 Each is surrounded by a splanchnic layer of the coelomic 



