32 C. IV. M. Poynter 



and the aortse, H. No. 939. During the next 36 hours of develop- 

 ment the picture remains the same, only new connections are being 

 established caudally and the anterior ones are dropping out, H. Nos. 

 562 and 559. This condition has been figured by Felix (1910) 

 and others for the human. 



Before " Wandenmg " is complete two or more small vessels 

 spring from the most proximal portion of the umbilical arteries to 

 supply the posterior limb buds, H. No. 560. Later these vessels 

 can be identified as the two primary limb vessels. The more 

 caudal vessel grows the more rapidly and soon seems to be the 

 continuation of the aorta of which the umbilical is a branch, H. 

 No. 658. I have not discussed the lateral shifting which Hoch- 

 stetter first described in 1890. 



The human embryo of the 11 mm. stage presents the condition 

 just described in embryo No. 1658, except that the umbilical 

 arteries are very much larger, Jackson embryo No. 68. About 

 this stage, my embryo 12 mm. and Jackson No. i, the hypogastrics 

 present a condition of " Wanderung," so that the junctions of the 

 umbilical and these vessels present broad areas of origin with 

 numerous roots. This is much later than the appearance of the 

 "abdominal plexus," 7 mm. stage, referred to by Senior (1919), 

 which may have persisted, although I did not identify such a 

 condition. 



My embryo 14 mm. and Jackson embryo No. 60, same age, show 

 the beginning of the pudendal and superior gluteal ; these buds 

 appear at the point of the " Insulbildung." By the 17 mm. stage, 

 Jackson embryo No. 58, the lateral sacral has appeared and a 

 branch passing medially toward the rectum. The latter is not 

 constant and could not be found in some of the later stages. ' Gen- 

 erally by the 19 mm. stage all connections between the branches has 

 disappeared so that each seems to arise separately from the umbil- 

 icals ; the " Insulbildung " occasionally persists for some time as in 

 the Jackson embryo No. 32 of 25 mm. 



From a study of these steps of development and the subsequent 

 stages up to 40 mm. it is evident that the way in which the different 

 connections persist or drop out will determine the arrangements of 

 the branches of the hypogastric. 



