LESSON XXV. 



THE KIDNEY. 



1. Dissection of sheep's kidney. It is advis- 

 able, before doing the microscopic work, to revive a 

 knowledge of the points of structure of the kidney 

 which can be seen with the eye. 



Cut a fresh kidney in two transversely to the long 

 axis and about one-third from the end; divide the large, 

 piece longitudinally along the convex border as far as 

 the pelvis. Note in the transverse and longitudinal 

 sections, the pale medulla formed by the pyramids 1 

 of Malpighi which project into the pelvis, outside 

 this, the intermediate layer, forming a dark red 

 zone not sharply defined, especially on the outer side, 

 and having pale stripes, the medullary rays, 

 extending into it from the pyramids of Malpighi; 

 stretching from this to the surface, the cortex, a 

 brownish-red zone ; the pale medullary rays continue 

 outwards in the cortex but do not reach the surface. 



Trace out the branches of the renal artery and 

 vein, they enter the kidney substance at the base of 



1 In some animals, e.g. rabbit and rat, there is only one pyramid, 

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