General Features 



2] 



Fig. 16. Diagrammatic transverse section of the body of a vertebrate showing 

 relations of organs to the peritoneum and coelom. (A) Dorsal aorta; (C) coelom; 

 (EN) endodermal epithelium of digestive tube; (G) gonad; (I) integument; (K) 

 kidney; (L) liver; (M) muscle layer of digestive tube; (MD) dorsal muscle of 

 body-wall; (MV) ventral muscle of body-wall; (NC) position of embryonic noto- 

 chord; (NT) neural tube (spinal cord); (PP) parietal peritoneum; (PV) visceral 

 peritoneum; (R) rib; (VC) vertebral column. (Courtesy, Neal and Rand: "Chordate 

 Anatomy," Philadelphia, The Blakiston Company.) 



body-cavity or coelom (Figs. 10, 16). The larger of these, the abdomi- 

 nal cavity, which occupies by far the greater part of the space within 

 the trunk, contains the stomach, intestine, liver, pancreas, kidneys, 

 reproductive organs, spleen, and other less conspicuous organs. In all 

 lung-breathing vertebrates except mammals, the lungs also lie in this 

 same cavity, which is then appropriately called the pleuroperitoneal 

 cavity. 



The second and much smaller cavity lies immediately anterior to 

 the abdominal or pleuroperitoneal cavity and in an extremely ventral 

 position. This is the pericardial cavity, which contains only one 

 organ, the heart. The thin membranous wall between the two cavities 

 is the septum transversum. 



In mammals the lungs lie in a pair of cavities, the right and left 

 pleural cavities, situated just anterior to the abdominal cavity and 

 on either side of the pericardial cavity (Fig. 17). The mediastinal 



