198 JOHN LEWIS BREMER 



The mesonephric arteries themselves in man differ from 

 those of other animals in the younger stages in that they are 

 much distorted and bent from their usual direct course by the 

 growth amongst them of the precocious suprarenal gland. Some 

 are deflected ventrally, some dorsally, so that they arise in two 

 more or less distinct vertical rows from the ventro-lateral and 

 dorso-lateral surfaces of the aorta, respectively. The suprarenal 

 vessels are the aortic roots between these two rows. The in- 

 frequent branches of mesonephric arteries to the suprarenal 

 gland may approach it from behind or from in front. 



An ascending branch from the upper suprarenal artery, or 

 from the upper end of the plexus, frequently becomes the inferior 

 phrenic artery; one or both of these vessels may be connected 

 with the coeliac axis or with a lumbar artery (cf. cat 15.6 mm., 

 mentioned on p. 196). A descending branch from the lower 

 suprarenal artery, or from the lower end of the plexus becomes 

 the permanent renal artery. This vessel can be traced to the 

 kidney in a human embryo of 16.0 mm. (H.E.C. No. 1322), 

 and in one of 16.4 mm. (H.E.C. No. 1707). Terminal branches 

 can be seen at the upper pole of the kidney in an embryo of 13.6 

 mm. (H.E.C. No. 839), but I am unable to trace with certainty 

 the course of the vessel in this specimen. 



In the 16.4 mm. embryo (fig. 10), the more ventral mesonephric 

 arteries sweep ventrally in front of the suprarenal gland, and then 

 turn laterally to reach the glomeruli. Dorsal to these, but con- 

 nected with them by occasional anastomoses, a set of branches, 

 represented by two roots on the right side of the figure, by one 

 large root on the other, passes to the suprarenal gland. The two 

 on the right have apparently just lost an anastomotic connection 

 at 'x,' while on the left side the plexus has been reduced to two 

 large longitudinal \ essels, each sending sprouts to the gland . 

 This left side of the figm'e resembles the reconstructions of rabbit 

 embryos made by Lewis, the longitudinal vessel representing 

 his 'renal artery.' At this level there are no mesonephric arteries 

 passing dorsal to the suprarenal gland. From the bottom of the 

 longitudinal trunk on the one side, from the lower end of the 

 lower suprarenal artery on the other, single vessels pass to the 



