688 



MANUAL OF PHYSIOLOGY. 



and splanchnopleure (pleuroperitoneal cavity), close to their 

 origin from the uncleft mesoblast, becomes columnar in character. 

 It receives the name of the germinal epithelium. An involution 

 of this takes place into the mesoblast, just below the somato- 

 pleure, and becomes shut off, and forms a hollow cylinder. 

 \ 



FIG. 278. 



m.p 



Transverse section through the lumbar region of an embryo chick at the end of the 

 fourth day. (Foster and Balfour.) W.R. Wolffian ridge, g.e. Germinal epithelium. 

 A.O. Dorsal aorta. M. Mesentery. SP. Splanchnopleure. d. Alimentary canal. V. 

 Vessels, m.p. Commencing MUIlerian duct. So. Somatopleure. W.b. Wolffian body. 

 W.d. Wolffian duct. V.c.a. Posterior cardinal vein. c.h. Notochord. A. W. C. Anterior 

 white column of spinal cord. o.r. Anterior root. A.G.G. Anterior gray column, p.r. 

 Posterior root. m.p. Muscle plate, nc. Canal of spinal cord. 



By this means a second duct is formed in close relation to the 

 first ; this is the Mullerian duct. This duct is developed from 

 before backward. 



