202 



THE ESSENTIALS OF HISTOLOGY. 



veins. The arteries of the cavernous tissue may sometimes in injected 

 specimens be observed to form looped or twisted projections into the 

 cavernous spaces (helicine arteries of Mutter). 



Urethra. The cross-section of the urethra appears in the middle of 

 the corpus spongiosum in the form of a transverse slit. It is lined in 

 the prostatic part by transitional, but elsewhere by columnar epi- 

 thelium, except near its orifice, where the epithelium is stratified scaly. 

 In the female urethra it is scaly throughout. The epithelium rests 

 upon a vascular mucous membrane, and this again is supported by a 

 coating of submucous tissue, containing two layers of plain muscular- 

 fibres an inner longitudinal and an outer circular. Outside this again 

 is a close plexus of small veins which are connected with, and may be 

 said to form part of, the corpus spongiosum. 



The mucous membrane of the urethra is beset with small mucous 

 glands, simple and compound (glands of Littre). There are also a 



number of oblique recesses termed lacunw. 

 Besides these small glands and glandular 

 recesses, two compound racemose glands 

 open into the bulbous portion of the urethra 

 (Cowper's glands). Their acini are lined by clear 

 columnar cells which yield a mucous secretion. 

 The prostate, which surrounds the com- 

 mencement of the urethra, is a muscular and 

 glandular mass, the glands of which are 

 composed of tubular alveoli, lined by colum- 

 nar epithelium, with smaller cells lying be- 

 tween them and the basement-membrane. 

 Their ducts open upon the floor of the 

 urethra. 



The integument of the penis contains 

 numerous special nerve end-organs of the 

 nature of end-bulbs, and Pacinian bodies 

 are also found upon the nerves. Lym- 

 phatic vessels are numerous in the in- 

 tegument of the organ and also in the sub- 

 mucous tissue of the urethra. 



The testicle is inclosed by a strong fibrous 

 capsule, the tunica albuginea (fig. 236, i). 

 This is covered externally with a layer of serous epithelium reflected 

 from the tunica vaginalis. From its inner surface there proceed fibrous 

 processes or trabeculce, which imperfectly subdivide the organ into 

 lobules, and posteriorly the capsule is prolonged into the interior of the 



FIG. 236. PLAN OF A VER- 

 TICAL SECTION OF THE TES- 

 TICLE, SHOWING THE AR- 

 RANGEMENT OF THE DUCTS. 



The true length and diameter of 

 the ducts have been disregard- 

 ed, a, a, tubuli seminiferi 

 coiled up in the separate lobes; 

 b, vasa recta ; c, rete vascu- 

 losum ; d, vasa efferentia end- 

 ing in the coni vasculosi; l,e,g, 

 convoluted canal of the epi- 

 didymis ; h, vas deferens ; /, 

 section of the back part of the 

 tunica albuginea ; i, i, fibrous 

 processes running between the 

 lobes ; / to s, mediastinum. 



