No. 408.] STUDY OF MAMMALIAN EMBRYOLOGY. 93I 
mesenchyma is the anlage of a vertebra (Ve77.). It is more 
expanded laterally than dorso-ventrall. In the median line 
below the notochord is the large dorsal aorta (Ao.), which is 
SP.C. 
Nch. 
; G. 
N. 
Vert. 
W.t. 
Som. 
Ao. 
D.V. W.B. 
Gen. 
Ec. 
Om.mayj. 
75. 
St. 
nsth. 
Li. 
Om.min. 
V.U.D. 
Un. 
V.U.SS. 
Fic. 7. — Pig of 12.0 mm. No.5. ‘Transverse section 633. 40., aorta; D.V., ductus venosus ; 
Ec., ectoderm of the somatopleure ; G., ganglion on dorsal root of spinal nerve; G.A., gall 
bladder; A e eni land; LZ, liver; mes., mesenchyma of somatopleure ; 
msth., mesothelium of the somatopleure; Mch., notochord; W., spinal nerve; ma 
omentum major; Om.min., minus; .So»r, somatopleure; Sż., stomach; 
umbilical cord; Vert., anlage of the body of a vertebra; V.U.D., right umbilical vein; 
.U.S., left umbilical vein; W.B., Wolffian body or mesonephros ; J/.7., Wolffian tubule. 
x 22 diams. 
formed by the union of the two dorsal aortic trunks of Fig. 6, 
and which extends through the abdominal region of the 
