CH. xxxvi.] THE URINARY APPARATUS. 529 



inhibited or relaxed, impulses pass to the muscles of the lower 

 intestine increasing their peristalsis, and to the abdominal muscles 

 as well. 



Both inhibitory and motor fibres for the lower part of the 

 intestine leave the cord by anterior roots lower than those which 

 contain the fibres for the small intestine. The cell-stations are 

 situated in the inferior mesenteric ganglia, or along the course 

 of the colonic or hypogastric nerves. The lower portion of the 

 large intestine resembles the oesophagus in being more under 

 external nervous control than the small intestine. 



CHAPTER XXXVI. 



THE URINARY APPARATUS. 



THIS consists of the kidneys ; from each a tube called the ureter 

 leads to the bladder in which the urine is temporarily stored ; 

 from the bladder a duct called the urethra leads to the exterior. 



The Kidneys are two in number, and are situated deeply in 

 the lumbar region of the abdomen on either side of the spinal 

 column behind the peritoneum. They correspond in position to 

 the last dorsal and three upper lumbar vertebrae ; the right 

 is slightly below the left in consequence of the position of the 

 liver on the right side of the abdomen. They are about 4 inches 

 long, 2^ inches broad, and ii inch thick. The weight of each 

 kidney is about 4^ oz. 



Structure. The kidney is covered by a fibrous capsule, which 

 is slightly attached at its inner surface to the proper substance 

 of the organ by means of very fine bundles of areolar tissue and 

 minute blood-vessels. From the healthy kidney, therefore, it may 

 be easily torn off without much injury to the subjacent cortical 

 portion of the organ. At the hilus of the kidney, it becomes 

 continuous with the external coat of the upper and dilated part 

 of the ureter (fig. 415). 



On dividing the kidney into two equal parts by a section 

 carried through its long convex border it is seen to be composed 

 of two portions called respectively cortical and medullary ; the 

 latter is composed of about a dozen conical bundles of urinary 

 tubules, each bundle forming what is called a pyramid. The 

 upper part of the ureter or duct of the organ, is dilated into the 

 pelvis ; and this, again, after separating into two or three principal 

 divisions, is finally subdivided into still smaller portions, varying 



K.P. M M 



