Fig. 105. — Pig Embryo of 12.0 mm. Reconstruction from the Transverse Sections, Series 5. 

 The figure illustrates chiefly the veins of the right side, and shows the right auricle and ventricle of the heart. 

 A, The right umbilical artery, only a small portion being drawn as it curves around the Wolffian duct, 

 IV. D. a, Tip of aortic septum, which divides the aortic limb of the heart into the pulmonary aorta, P, 

 and main aorta, Ao ; by a growth of the cardiac tissue, a, />, and c of the figure become joined, shutting oft 

 the space around the base of the aorta ; this space communicates by the interventricular foramen with the 

 left ventricle, and serves as the permanent or adult channel of communication between the true aorta, Ao, 

 and the left ventricle. All, Allantois. Ao, Aortic division of the aortic limb of the heart. Au, Right 

 auricle, b. See "a." c, See "a." card', Superior part of the cardinal vein (the anlage of the azygos). 

 card''. Inferior part of the posterior cardinal vein, cl.i, Opening of the first gill pouch into the pharynx, 

 the pharynx being indicated by dotted shading, cl.2. Opening of the second gill pouch into the pharynx. 

 cl.j, cl.^, Entodermal portions of the third and fourth gill clefts, com. Dotted outline of the omental 

 or lesser peritoneal cavity, d. Left duct of Cuvier. D. C, Right duct of Cuvier, the main venous trunk 

 entering the heart from the right side. D. V, Ductus venosus Arantii. F. IV, Foramen of Winslow, 

 drawn in black. ^.//, Foramen, drawn in black, between the pleural and peritoneal cavities. Gen, Genital 

 tubercle, represented as somewhat displaced from the median line, which it really occupies. G./i, Genital 

 ridge. Jug' , Ji^g" ■, Jugular or anterior cardinal vein. Li, Liver, l.s, Anlage of the lateral venous sinus. 

 mx. Vein of the inferior maxilla or mandible. P, Pulmonary division of the aortic limb of the heart. 

 p.c. Pericardial cavity. PI, Dotted outline of pleural cavity. Rec, Rectum. Sc, Subcardinal vein, which 

 is derived from the cardinal and on the right side of the body forms part of the vena cava inferior. Scl, 

 Subclavian vein, sis, Anlage of the superior longitudinal venous sinus, which is formed by the union of the 

 veins, l.s., from the sides to make a single vessel between the cerebral hemispheres. Ur, Ureter. Um.d, 

 Right umbilical vein, v. Valve of the sinus venosus. Ven, Right ventricle of the heart. V.H.C, Vena 

 hepatica communis, v. op. Ophthalmic vein. V.P, Portal vein. IV.b, Wolffian body. W.D, Wolffian 

 duct. X, Anastomosis between the cardinal venous systems of the right and left sides. X ^4 diams. 

 — [Drawn by Dr. F. T. Lewis.) 



