236 STUDY- OF PIG EMBRYOS. 



Li, extends to the umbilicus; the smaller dorsal lobe, Li 1 , abuts against the Wolffian 

 body. In the fresh specimen the liver is conspicuous by its dark color. The 

 Wolffian body, W.B, is very large; it extends from the dorsal edge of the dia- 

 phragm to the level of the hind limb, H.L, or, in other words, to the pelvic end 

 of the abdomen. The Wolffian tubules can be seen running transversely just 

 within the surface of the organ and nearly parallel to one another. The large 

 size of the Wolffian body (fetal kidney or mesonephros) is characteristic of all 

 known amniote embryos. The umbilical cord projects upward from the ventral 

 wall of the abdomen; its cut surfaces, Um, are indicated by parallel lines. The 

 abdominal cavity extends into the cord, forming the umbilical coelom, Cc&. From 

 underneath the liver and on the right side of the embryo, the small intestine, //, 

 runs out into the umbilical coelom, makes a sharp loop turn, and passes over into 

 the large intestine, Col, which runs back to the abdomen on the left side of and 

 nearly parallel to the ileum, //; it passes under the tip of the liver, then between 

 the two Wolffian bodies, where it curves in the median plane though this is not 

 shown in the figure and, bending tailward, terminates in the cloaca, Clo. From 

 the tip of the intestinal loop springs the stalk, Yk.s, of the yolk-sac. The begin- 

 ning of the large intestine is marked by a small knob, CCKC, the anlage of the 

 csecum. At this stage the small and large intestines are of about the same di- 

 ameter. From the cloaca, Clo, a hollow prolongation, All, runs out into the caudad 

 wall of the umbilical cord; it is the stalk of the allantois. 



Anatomical Reconstructions from the Sections. Six reconstructions of the anatomy 

 of this stage are figured.* Figures 171, 173, 174, 175, 177, and 179 are based 

 on the same series which has supplied the transverse section of the 12 mm. pig 

 figured in the following pages. . The umbilical cord of this embryo (Series 5) 

 having been damaged, the loop of the intestine in the umbilical cord has been 

 added to figures 171 and 174 by a reconstruction from another series (No. 518) of 

 an embryo of the same size. 



The following remarks call attention to some of the more important anatomical 

 relations shown by the reconstructions. The great volume of the central nervous 

 system as compared with the remaining parts is very striking. Of the other 

 organs, the three which are most conspicuous by their size are the heart, liver, . 

 and Wolffian bodies. Another striking peculiarity of the embryo is the great 

 diameter of the blood-vessels, and especially of the veins, which are of relatively 

 enormous diameter, being proportionately much larger than in the adult. In 

 marked contrast with this is the small diameter of the cavity of the trachea and 

 lungs and of the entire intestinal canal. 



Figure 172 represents in the main a median section of the embryo together 



* Figures 171, 175, 177, and 179 were made by Dr.F. T. Le\v;s; figure 174 by Mr. P.P. Johnson; figure 173 

 is from a wax reconstruction by Dr. John L. Bremer. In all cases the reconstructions were made with special 

 reference to their present use. It gives me much pleasure to acknowledge my obligations to these members of 

 our laboratory staff. 







