The Development of the Alligator Z'^'] 



{hi), which here consist of several thick-walled 

 tubes, surrounded by lobes of mesoblast. The 

 other features of the figure need no special mention. 

 Figure 207 is through the base of the posterior 

 appendages {pa) , in which the cartilages are already 

 being outlined by condensations of mesoblast. The 

 intestine (i) is cut in two regions — at a more an- 

 terior point, where it is seen as a small, circular 

 hole surrounded by mesoblast and hung by a 

 narrow mesentery, and through the cloacal region, 

 the larger and more ventral cavity, into which the 

 Wolffian ducts {wd) open a short distance caudad 

 to this section. The blood-vessels present a rather 

 curious appearance. A short distance anterior to 

 this point the aorta has divided into three, or it 

 might be said that it has given off two, large 

 branches. These two branches, one on either side 

 near the posterior cardinal vein, pass toward 

 the ventral side of the embryo on each side of the 

 cloaca and end at about the region represented by 

 the present figure. The small portion of the aorta 

 that remains after the giving off of the two 

 branches just described continues, as the caudal 

 artery {ca), into the tail; it is a small vessel just 

 under the notochord, and gives off small, paired 

 branches at regular intervals toward the vertebral 

 region. The posterior cardinal veins {pc) , posterior 

 to the openings of the Wolffian ducts into the 

 cloaca, unite to form a large caudal vein lying just 

 ventral to the caudal artery. 



