180 JOHN LEWIS BREMER 



one can readily understand the rare cases in which the right and 

 left accessory renal arteries both spring from the inferior mesen- 

 teric artery, or both arise from a common stem from the aorta 

 below that vessel. Such a case has been reported and figured 

 recently by Harvey (3). 



This class of anomaly may be considered thus separately be- 

 cause it has no relation to the question of the origin of the nor- 

 mal adult renal artery. The plexus described does, however, 

 give a valuable clue to other anomalous conditions. What then 

 is the origin of the permanent renal artery? 



Broman (4) and others have stated that in man the renal 

 artery is the trunk of a former mesonephric vessel, utilized sec- 

 ondarily as the inferior suprarenal artery, and finally as the 

 renal artery, with the suprarenal as a branch. On the other 

 hand, Hochstetter (5), Hill (6), and others have maintained that 

 in mammals other than man, the renal arterj' is normally a new 

 branch from the aorta at about the time when the kidney has 

 reached its permanent position. Hill places this^at 28.0 mm. in 

 the pig, at which age he succeeded in injecting this vessel, but 

 states in another paper that in man the vascularization occurs 

 between 22.0 and 24.0 mm. No explanation has been offered 

 for the peculiarit}^ of man in this respect, and in fact very little 

 corroborative work has been done on this subject. This is all the 

 more strange because the conception that a new vessel can 

 sprout from a well established trunk, as stated by Hochstetter 

 and Hill, is contrary to the modern ideas of vessel growth. Yet 

 other writers also, notably Kolster (7) , at a loss to explain certain 

 renal anomalies, have fallen back on the supposition of a 'late 

 branch' from some neighboring vessel. 



The aorta of pig embryos much smaller than 28.0 mm. is pro- 

 vided with a well differentiated coat of modified mesenchyma, 

 the future tunica media, through which the endothelium of a new 

 branch would have to force its way. Now endothelium may and 

 does sprout abundantly, but only in the looser, undifferentiated 

 mesenchyma, or in its derivative, loose connective tissue. A 

 slight condensation of the mesenchyma, as in the incipient so- 

 mites, makes the ingrowth of endothelial sprouts impossible, and 



