608 SPECIAL HISTOLOGY. 



medium-sized fibres, and is covered with a laminated epithelium 0*03- 

 0-05 of a line thick, whose deeper elements are usually fusiform, conical 

 or cylindrical, the more superficial, rounded-polygonal, or flattened. 

 They exhibit the same want of uniformity in size as those of the pelvis 

 of the kidney, to which irregularity the numerous depressions of various 

 depths on the under surface of the uppermost cells, for the reception of 

 the ends of the deeper, elongated cells, much contribute; peculiar 

 stellate and dentate forms being thence produced. In the neck of the 

 bladder and towards i\\Q fundus, there occur mmwiQ glands, in the form 

 of simple pyriform follicles, or small aggregations of these (simple 

 racemose glands). These glands, 0-04-0-24 of a line in size, have 

 orifices of 0-02-0'05 of a line, a cylindrical epithelium, and contain a 

 clear nnicus. In pathological conditions, as Virchow informs me, they 

 are occasionally enlarged and filled with whitish mucous plugs. 



The 7nale urethra will be described w'ith the sexual organs. That of 

 the female presents a reddish mucous membrane with numerous vessels, 

 especially in the form of much-developed venous plexuses in the sub- 

 mucous tissue (which Kobelt, without any reason, has described as a 

 corjyus spongiosum), and a squamous epithelium, the deeper-seated cells 

 of which are elongated, as in the bladder. There is an external mus- 

 cular tunic united with the mucous membrane, consisting of a thin 

 layer of longitudinal and transverse smooth muscles, intermixed with 

 much connective tissue and elastic fibres, and of the thick substance of 

 the musculus urethralis, the direction of the fibres in which is chiefly 

 transverse. A certain number of larger and smaller racemose mucous 

 glandules ("glands of Littre"), resembling in their structure those of 

 the bladder, except that they are usually somewhat larger and more 

 closely placed, pour their secretion into the urethra. Occasionally 

 these glands occur of larger size (as much as 2 lines), and prominent, 

 containing a colloid-like material in the distended vesicles. 



§ 191. Pliysiological remarks. Development of the urinary organs. 

 — According to Remak, the kidneys in the Chicken are formed as two 

 protrusions of the intestine, in the constitution of which the epithelial 

 and the fibrous layers both take part, and, like the lungs, grow by the 

 ramification of their epithelial tube, and the augmentation in bulk of 

 the fibrous layer (Unters. z. Entw. d. Wirbelth. Tab. II., fig. 83-85). 

 In the Mammalia, the earliest stage of the development of the kidneys 

 has not yet been observed ; but what we do know from the labors of 

 Rathke, J. Mliller, Valentin, and Bischofi", with respect to its subse- 

 quent conditions, perfectly accords with the statements of Remak, 

 except that, in this case, the glandular canals appear to be developed 

 upon the type of the salivary glands,, and are not hollow from the com- 

 mencement. The rudimentary kidneys in the Mammalia, at first, 



