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LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



opening to the exterior, the blastopore, which is situated at the future posterior end of th 

 embryo. This entodermal tube persists as the lining of the adult digestive tract and of all o 

 its derivatives; to it there are added other layers (connective tissue and muscular layers 

 derived from the splanchnic mesoderm of the hypomere, which, it will be recalled, folds arounc 

 the archenteron. The adult digestive tract thus consists of a thick-walled tube, composed o 



Fig. 45. — Diagrams to illustrate the divisions of the coelom in the various vertebrate classei 

 The transverse septum and its derivatives are indicated by thick lines. A, fishes, showing the divisio 

 of the coelom into pericardial cavity a and pleuroperitoneal cavity g by means of the transverse septum c 

 B, urodeles, similar to fishes with the addition of the lung h which projects into the pleuroperitone; 

 cavity g. C, turtle; the pericardial cavity has descended posteriorly until it lies ventral to the anteric 

 part of the pleuroperitoneal cavity g: the anterior face of the transverse septum d has now become pai 

 of the wall of the pericardial sac; the lung k is retroperitoneal. D, early stage of mammals, showing tl 

 beginning of the coelomic fold (pleuroperitoneal membrane) j descending from the dorsal body wall, an 

 the liver/ inclosed within the transverse septum d. E, later stage of mammals, showing union of tl 

 coelomic fold/ with the transverse septum d, the two together forming the diaphragm which separati 

 the pleural cavity k from the peritoneal cavity m; the liver has constricted from the main part of tl 

 transverse septum, the constriction becoming the coronary ligament /. a, pericardial cavity; 6, hear 

 c, parietal pericardium or pericardial sac; J, transverse septum; e, serosa of the liver, this being a pa 

 of the transverse septum originally; /, liver; g, pleuroperitoneal cavity; A, lung; /, coronary ligamei 

 of the liver; j, coelomic fold which forms part of the diaphragm; k, pleural cavity; I, pleuropericardi 

 membrane or anterior continuation of the transverse septum; in, peritoneal cavity. 



both entodermal and mesodermal elements, the latter predominating. The anterior ar 

 posterior ends of the digestive tube are formed by the invagination of the surface ectoden 

 that at the anterior end which becomes the lining of the mouth cavity being called the stom 

 dacum, that at the posterior end, lining the anus, the proclodacum. 



