TRANSVERSE SECTIONS OF EMBRYO OF 12 MM. 



197 



ries. By an oversight the two arteries are represented as one in the engraving. 

 To the right and left of the oesophagus appear the circular sections of the two 



Sp.c. 



D.R, 



Nch. 



Som. 



FIG. 120. PIG, 12. o MM. TRANSVERSE SERIES 5, SECTION 470. 



Ao.S, Left descending aorta. Au.d, Right auricle. Br.Plx, Brachial plexus. D.C.S, Ductus Cuvieri 

 sinistra. D.R, Dorsal root of spinal nerve. F, Cardiac fissure. G, Spinal ganglion. Z, Anterior limb-bud. 

 Nch, Notochord. Nv, Branch of brachial plexus. (E, (Esophagus. R.D, Ramus dorsalis of spinal 

 nerve. S.a.c, Septum of the auricular canal. Scl.V, Subclavian vein. Som, Somatopleure. Sp.c, Spinal 

 cord. S.s, Septum superius. Tra, Trachea. Val, Auriculo-ventricular valve. Ven.S, Left ventricle of 

 the heart. V.R, Ventral root of"spinal nerve. X 22 diams. 



descending aortae, of which ttfl'left, Ao. S, is already somewhat larger than the 

 right. Ultimately the greater part of the right aorta will disappear, the aortic 



