84 MORPHOLOGICAL TYPES 



highly vascular walls surrounding a cavity which is subdivided 



Fig. 41. — Ceratodus : diagram of the relations of the lung, heart, and 

 vascular system seen from the ventral side (combined from diagrams 

 after Baldwin Spencer, simplified). 



aa, anterior abdominal vein ; ab, afferent branchial artery ; b, brachial 

 vein ; ea, efferent branchial artery ; ej, external jugular vein ; g, glottis ; 

 ijt internal jugular vein ; /, lung ; la, left auricle ; //, left lateral abdominal 

 vein ; Ipa, left pulmonary artery ; Ipc, left posterior cardinal vein ; o, 

 oesophagus ; p, pharynx ; pv, pulmonary vein ; rl, right lateral abdominal 

 vein ; rpa, right pulmonary artery ; rpc, right posterior cardinal vein 

 (remnant) ; rvcs, right vena cava superior ; t, truncus arteriosus ; vci, 

 vena cava inferior. 



into little chambers or " cells." In the lung the blood can be 

 oxygenated when the water in which the animal lives becomes 



