578 URINARY APPARATUS. 



the neck, properly so called, is continuous with the urethra (Fig. 344). At birth, 

 this anterior neck separates from the urachus, and is transformed into a free cul- 

 de-sac ; while the bladder is gradually withdrawn into the pelvic cavity, carrying 

 with it the umbilical arteries, and finishes by acquiring the position it definitively 

 occupies in the adult. 



Functions. — The part played by the bladder is of incontestible utility. In 

 permitting the accumulation of the urine and the intermittent expulsion of that 

 excrementitial fluid, it spares animals the disagreeable condition in wliich they 

 would be placed if the hquid secreted by the kidneys was continually being dis- 

 charged as produced. 



4. Urethra. 



The description of this organ will be given with that of the genital organs, 

 as in the male it is common to the urinary and generative apparatus ; even in the 

 female it is intimately connected with the latter. 



5. The Supra-renal Capsules (Fig. 338, 344). 



Situation — Form. — The supra-renal capsules (or adrenals) are two small bodies 

 applied to the lower face of the kidneys, in front of the hilus, and close to their 

 inner border. 



They are elongated from before to behind, flattened above and below, and 

 irregularly lobulated on their surface. Their length is from 2 to 23 inches, and 

 width from li to H inches. They have not the same volume, the right being 

 larger than the left. 



delations. — A large amount of connective tissue, vessels, and nerve-filaments 

 attach these bodies to the neighbouring organs. The right is related, in front, 

 to the liver ; above, to the right kidney ; and inwardly, to the posterior vena cava 

 and the ramifications of the solar plexus. The left does not touch the liver or 

 spleen, but, by its inner border, is applied against the posterior aorta and great 

 mesenteric artery. 



Structure. — At present, anatomists are not agreed as to the structure of the 

 supra-renal capsules. The following is what is probably most reliable in this 

 difficult point in normal histology. 



These organs offer an enveloping membrane and parenchyma. 



The enveloping membrane is fibrous, and sends off, from its inner face, prolon-« 

 gations which pass into the parenchyma and form cylindrical spaces, subdivided 

 by transverse bands. These spaces are named glandular cavities ; but the septa 

 soon become thin, and disappear almost completely, leaving nothing but some 

 very few trabeculse of connective tissue. 



The parenchyma is divisible into two layers — the cortical and the medullary 

 substance. The first is of a dark-brown colour ; the second is yellow and soft, 

 and does not show any cavity in its centre ; that which has been described is the 

 result of the destruction of its proper elements, which soon change after death. 



The glandular cavities of the cortical substance are filled with nucleated, 

 granular, and often fat cells, in the adult animal ; near the central substance 

 these cavities only contain a single cell. 



The medullary substance has, for its basis, a very dehcate reticulum, support- 

 ing stellate cells analogous to those of nerve-tissue. 



and nerves. — Like the kidneys, which are contiguous, the supra-renal 



