THE URINARY SYSTEM 409 



691. The Medulla is paler in colour than the cortex, and on the 

 whole is more dense in its structure. It consists of cone-shaped 

 masses, the points of which are directed towards the centre of the 

 gland, where an irregularly shaped cavity, known as the pelvis or 

 basin of the kidney, is found. These cone-shaped bodies are, in 

 reality, bundles of uriniferous tubes. 



692. Briefly, the urine is secreted by the Malpighian bodies and 

 certain portions of the uriniferous tubes from the arterial blood, 

 supplied by the renal artery ; it then passes through these uriniferous 

 tubes into the basin of the kidney, and thence into the ureters, which 

 convey it to the bladder. 



693. Suprarenal Capsules.— These are two little glandular 

 bodies attached to the front borders of the kidneys ; they are ductless, 

 and their use is not well known. 



694. The Ureters {Plate XV III., I I, and Plate XLL, A 3 3) 

 are two tubes running from the basin of each kidney to the bladder, 

 and, as before stated, their function is to carry the urine from the 

 kidneys to the bladder. They enter the bladder obliquely at the 

 upper and back part, and in this way a kind of valve is formed, by 

 which urine is prevented from flowing back from the bladder into 

 the ureters. 



695. The Bladder {Plate XVIII. , K, and Plate XLL, A 4, and 

 B 5) is a musculo-membranous sac or bag found in the pelvic cavity. 

 Its function is to receive and retain the urine until a sufficient 

 quantity has been collected for expulsion. In this way a constant 

 dribble of fluid is avoided. Structurally, it is made up of three 

 coats, and consists of a fundus, body, and neck, and it is held in position 

 by means of ligaments. The bladder, when distended with urine, is 

 pear-shaped, and extends into the abdominal cavity. On the fundus 

 a scar or cicatrix is seen, which is all that remains of the urachus, 

 the tube by which the urine is carried, by way of the umbilical cord, 

 to the placenta during foetal life. The neck of the bladder passes 

 backwards, and terminates in the urethra. 



