FIG. 172. PIG EMBRYO OF 12.0 MM. RECONSTRUCTION FROM THE TRANSVERSE SECTIONS, SERIES 5. 



For the most part the organs represented are in or near the median plane. The drawing illustrates especially 

 the .disposition of the alimentary tract, the arterial system, and the heart. A. has, Basilar artery, formed by 

 the union of the two vertebral arteries, A .v, and joined, under the mid-brain, by the anterior ends of the internal 

 carotids. A.cau, Caudal artery, the small median prolongation of the dorsal aorta. All, The allantois; 

 it is joined by the Wolffian duct, and empties into the cloaca, an.pl, The cloacal membrane. Ao, Median 

 dorsal aorta. Ao.d, Right descending aorta; a small vessel connecting the dorsal ends of the third (carotid) 

 and fourth aortic arches. Ao.D, Main right descending aorta, passing downward to join its fellow and form 

 the median aorta. A.s, Subclavian artery. Au, Left auricle of the heart. A.unt, The umbilical artery 

 which runs in the mesodermic wall of the allantois and joins the caudal end of the dorsal aorta. A .v, Vertebral 

 artery. "A.vi, The vitelline artery, which becomes the superior mesenteric artery of the adult, c, Artery 

 known as~lh'e cceliac axis in the adult, car.e, External carotid artery, arising from the base of the third aortic 

 - arch. car. i, Internal carotid artery. Cbl, Cerebellum, d, Left duct of Cuvier. Dien, Diencephalon. D.V, 

 Ductus venosus Arantii. ep, Small plug of entodermal epithelium in the rectum; there are several small 

 irregular passages through the plug. Epgl, Anlage of the epiglottis. /, Interventricular foramen, opening into 

 the space a, b, c, of Fig. 176. F. M, Foramen of Monro. f.o, Foramen ovale, between the cardiac auricles, 

 "-bladder. In, Entodermal wall of the intestine, is, One of the series of intersegmental arteries, 

 ^'ind end of the ureter, the anlage of the renal pelvis. Lar, Anlage of the larynx, consisting 

 lial plate. Li, Liver. Lu, Entodermal portion of the lung. M.b, Mid-brain- Md.ob, 

 >7 \ A spinal nerve. Neu, Neuromeres of the hind-brain. Oe, (Esophagus, op, Stalk. 

 Ik is the anlage of the optic nerve. P. A, Pulmonary artery, pan, Dorsal anlage 

 art of which becomes the duct; behind the duct is the anlage of the ventral pan- 

 >wth from the duct of the gall-bladder, p.c, Pericardia! cavity. P.V, Pul- 

 SV, Stomach; the letters are placed beside the diverticulum which is char- 

 Mi man. t, Posterior portion of the tongue, an eminence on the floor of 

 >: ie ventral ends of the third and fourth gill-arches. T.i, Tuberculum 

 i of the tongue. Tra, Entodermal trachea. Ug.si, Cloaca. Um.d, 

 icle, the letters being placed on the septum inferius. V.mes, Superior 

 .7';, Vitelline vein. W.Dj Wolffian duct, x, Anastomosis between 

 ins. Yk, Yolk-sac. Yk.s, Entodermal yolk-stalk, connecting the 

 ^-(Draum by F. T.Lewis.) 



