DEVELOPMENT OF ARTERIES IN FORELIMB OF PIG. 151 



Elze (1907) takes issue with the views of Muller (1904). He investigated 

 the subclavian in four human embryos of 7, 9, 11, and 15 mm. In all, the sixth 

 segmental (seventh of others) forms a subclavian which crosses the plexus in the 

 region of the seventh cervical nerve. He finds no axillary net. He believes that the 

 original polysegmental supply is quickly reduced to a single vessel and he regards 

 the plexus axillaris of Muller as a secondary formation which has nothing to do 

 with the segmental arteries. The finding of two subclavians in the human embryo 

 is not an isolated one; Keibel and Elze described a second and Evans (1908) a third. 

 These vessels belong to successive segmental arteries and end in the capillary net 

 in the arm. 



The original net character of the arterial primordium is appreciated in the 

 work of De Vriese (1902). The material used consisted of 25 human embryos 

 between 10 and 100 mm., supplemented by other mammalian material. She 

 describes each nerve as being surrounded by a net and out of these nets are formed 

 the stems. In the forelimb mass a net is present for the median and the interosseous. 

 A stem in the interosseous strip becomes thicker and forms the primitive chief 

 artery, which loses this role through the development of the median. 



Goppert (1905) described his entire arterial system of the limb-mass as being 

 preceded by a net-formation which lies near to all peripheral nerve-fibers. In 1910 

 he presented his studies on the development of the arterial variations and in his 

 paper he gave a copious survey of the literature on this subject. His own investiga- 

 tions were made upon the white mouse. In his stage 1, which consists of five 

 embryos fixed and studied 8 days after impregnation, he finds the limb-mass sup- 

 plied by a number of branches varying from two to five, arising from the aorta. 

 These correspond and are usually segmentally arranged, but occasionally a branch 

 arises in a non-metameric position. 



All of our specimens show the early branches to the limb-bud arising as lateral 

 branches from the segmental arteries. In the pig no evidence is found of arteries 

 supplying the limb-mass that are not segmentally arranged, and herein our speci- 

 mens fail to agree with the findings of Evans in the duck and Goppert in the mouse. 

 Neither can we corroborate the great variability in number and arrangement which 

 Goppert so emphasizes. Furthermore, in all of our specimens the limb-arteries 

 appear as lateral branches of the dorsal segmental and not as lateral branches of 

 the aorta. 



Goppert's stage 2 shows the suppression of most of the lateral branches and the 

 elevation of one of them (the seventh) to the principal axial stem. The remnants 

 of the preceding and succeeding segmentals still persist. In the limb-mass the 

 principal artery breaks up into many branches. In the third stage the arteries 

 to the limb-mass may be single or still multiple and have now fused with the dorsal 

 segmentals. Whether single or double, they go through the third root of the 

 brachial plexus and form a branch medial and lateral to the plexus. These fuse 

 beyond the plexus. Thereafter the artery lies in the angle between the dorsal 

 and ventral nerves. It continues in the axis of the limb and finally breaks up into 

 numerous branches. The stem artery may show island-formation. 



