XXII.] STRUCTURE OF THE KIDNEY. 229 



the connective tissue outside the ureter and 

 pelvis; both artery and vein divide into 

 several branches which enter the substance 

 of the kidney outside and between the ends 

 of the calices at the bases of the pyramids; 

 tracing them outwards they will be seen to run 

 to the outer portion of the intermediate-layer 

 and there to branch, their branches arching 

 through the kidney substance and so forming 

 a net-work (more complete in the veins 

 than in the arteries) stretching through the 

 kidney substance in the curved surface of the 

 outer part of the intermediate-layer. 



2. From a mammalian kidney hardened in ammo- 

 nium bichromate 5 p.c. prepare radial sections 

 extending from the outer surface to the summit 

 of a papilla. The sections are best cut with a 

 .microtome. Stain them. Observe under a low 

 power. 



a. The medulla^ with its straight tubes ; some 

 of the numerous divisions of these as they 

 run outwards may be seen. 



h. The intermediate layer: the straight tubes 

 of the Malpighian pyramids separate into 

 bundles the medullary rays (pyramids of 

 Ferrein); between the bundles are seen 

 numerous blood-vessels and some tubes of 

 Henle (cp. § 3, 6). 



c. The cortex ; the medullary rays are seen to 

 run out nearly to the free surface, between 



