THE URINARY TRACT. 133 



apex rests upon the sinus, and by its encroachment upon this .struc- 

 ture produces a papilla. The base of the pyramid is capped by the 

 cortical arch. 



The sinus is the cavity at the basal portion of the kidney. The 

 opening into this cavity is the hilum. The cavity itself is formed 

 by a union of the excretory ducts, thus producing one large lumen, 

 and is invested with a coat which is continuous with the capsule 

 of the kidney, and within this is the wall, which is continuous with 

 that of the ureter. The space within this capsule is the pelvis. 



THE URETER. 



This structure is composed of three coats mucous, muscular, 

 and fibrous. The mucous membrane is lined with the so-called tran- 

 sitional epithelium, which consists of few layers, the deeper layers 

 being columnar, and those next the lumen, squamous. 



THE BLADDER. 



The bladder has three coats mucous, muscular, and fibrous. The 

 mucous coat is lined with stratified transitional epithelium, the cells 

 presenting considerable irregularity in shape, and often possesssing 

 more than one nucleus. 



THE URETHRA. 



The urethra consists of mucous and muscular coats. The mucous 

 coat of the female urethra is lined throughout with stratified squa- 

 mous epithelium. In the male urethra the prostatic portion is lined 

 with transitional epithelium, the intermediate part with stratified 

 columnar cells, while these are succeeded in the penile portion by 

 simple columnar cells. 



Laboratory exercise No. 42. The kidney. Harden with alcohol, em- 

 bed in paraffin, and stain with haematoxylin and eosin. Upon the onter 

 surface of your section observe the capsule, and beneath this a delicate 

 layer of smooth muscle. Distinguish between the cortex and medulla. 

 Observe the Malpighian pyramids of the medulla. Their apices form 

 the papillae, and their bases extend toward the periphery. What ele- 

 ments enter into their structure? The spherical, deeply-stained masses 

 in the medulla are the Malpighian bodies. Demonstrate the capsule of 

 Bowman and glomerulus; also the structure of a tubule, noting its 

 basement membrane, epithelial cells, and lumen. Make a study of 

 other structures enumerated in the outline of this organ. Drawings. 



