30 THE STRUCTURE OF MAN 
mencing fusion between the last two of these sometimes occur. 
Six vertebre were once observed in a boy four weeks old; and 
C.U. 
Fic. 204.—DIAGRAMMATIC RECONSTRUCTION OF THE TAIL END OF A 
Human Embryo (length of trunk, 8 mm.) 
ch., notochord ; ”., Wolffian tubule ; w., duct of primitive kidney ; ai’, intestine ; OJ’, 
urinary bladder ; m.a., anal membrane ; md, medullary tube; ad’, post-anal gut ; 
bl’, neck of allantois ; c.w., umbilical cord. (After Keibel.) 
C.C. 
a.C. 
md ll 
Fic. 20B.—DIAGRAMMATIC RECONSTRUCTION OF THE TAIL END OF A HuMAN EMBRYO 
YOUNGER THAN Fic. 20a (entire length, 4 mm.). (After Keibel.) 
Lettering as above ; in addition c.c., caudal limit of the celom ; a.c., caudal limit of the 
hind-limb ; i-ii, line drawn through the anterior limit of the tail. 
Leboucq has recorded the same number in an embryo 25 
mm. long. The opposite extreme is reached where only three 
