24 CHORDATA, 
avity of the myotome) early disappears and the ventral 
lement alone persists as a continuous perivisceral cavity. 
Fig. 306.—DIAGRAMMATIC TRANSVERSE SECTION THROUGH A 
LATER VERTEBRATE EMBRYO. 
(Mainly after VAN W1JHE.) 
Nerve Cord, 
er, 
Mesonephric 
Tubules, 
Pronephric Duct. 
Intestine. y 
Perivisceral Ccelom. 
Fig. 307.—THE PARTS OF THE Ca:LOM IN THE THORACIC 
CAVITY OF A MAMMAL. 
(After WIEDERSHEIM.) 
Vertebra. 
- 
Somatic Layer 
of Pleura. 
Trachea, isceral Layer 
Lung. Yi; of Pleura. 
( B 
A ‘ % 
Lung. 
‘ t Ny 
mae < ae 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. 
n the cavity lie the heart and all the alimentary organs. 
‘ach is surrounded by a splanchnic layer of the ccelomic 
