THE GESITAL ORGANS OF THE MALE. 971 



united by the abundant loose connective tissue in this part of the pelvis ; below, 

 it lies on the internal obturator muscle ; laterally, it is related to the muscles 

 and ligamentous or aponeurotic expansions that close in the sides of the pelvis. 

 Outside the pelvic cavity, the urethra is united in the most intimate manner 

 to the corpora cavernosa, which embrace its anterior border. By its posterior 

 border, it is related to the suspensory ligament of the penis. 



Structure, — The urethra is composed of : 1. Mucous membrane. 2. An 

 "'•p'^f He envelope, 'd. Jlusdes. 4. Vessels and nerves. 5. The perineal aponeuroses, 

 h are in immediate relations with this canal. 



. Mucous Membrane. — This is rather delicate, and forms the lining of 

 t ;anal. It is continuous, posteriorly, with that of the bladder, and in front 

 M 1 the integument enveloping the head (i/lans) of the penis ; it is also 

 prolonged into the excretory ducts of the glands annexed to the urethra, and the 

 ejaculatory ducts. It has longitudinal folds, and is always in contact with 

 itself, except during the passage of urine or semen ; it has scarcely any papillse, 

 only a few being found near the anterior extremity of the canal ; and its tissue 

 is very rich in elastic fibres. 



The epithelium of this membrane is stratified and cylindrical, but at the 

 portion furnished Avith papilla? it becomes pavemental. 



2. Erectile Envelope. — This envelope, lying outside the mucous membrane, 

 does not cover the intra-pelvic portion of the canal. It commences a little above 

 the ischial contour, behind Cowper's glands, by a very thick bulging portion, 

 named the bulb of the urethra. In front, it terminates by another bulbous 

 enlargement, into which the anterior extremities of the corpora cavernosa enter, 

 named the head of the penis (glans penis). 



The tissue composing this envelope has the same organization as other 

 erectile apparatuses, being a network of communicating cavities separated by 

 elastic septa, the latter showing in their structure some contractile elements (see 

 Corpora Cavernosa). 



3. Muscles. — Behind the prostate gland, the mucous membrane of the 

 urethra is covered by a fleshy layer of circular fibres, forming a sphincter. 

 Another musculr- envelope, constituting the bul bo-cavernous or accelerator urince 

 muscle, also co\ the erectile tissue of the urethra, accompanying it to near 

 the glans, where it gradually disappears. To these two principal muscles of the 

 urethra are added two pairs of secondary fasciculi — the compressor of Gouper's 

 glands and the transversus perinoei. The following is a resume description of 

 the muscular apparatus : — 



a. Urethral sphincter.^ — This may be described as a single muscle composed 

 of two portions — an inferior and a superior. Both are formed by transverse 

 fibres thrown over the membranous portion of the urethra, and both — the 

 superior and inferior — are united at their extremities, which are not attached to 

 the walls of the pelvis. Behind, the superior fibres are mixed with those of the 

 compressor of Couper's glands. 



b. Accelerator urinoe. — Composed of transverse fibres encircling the urethra 



' Up to tlie present, this organ lias been described in books on Veterinary Anatomy as 

 Wihoiis muscle. In a work entitled Becherches sur I'Anatomie mmparee du Perin^e, published 

 in Professor Robin's journal, Paulet riglitly objects to this designation, which perpetuates aa 

 error of interpretation. We adopt this opinion, not only with regard to this muscle, but also 

 the ischio-urethral, which, with him, we more exactly designate 8ts the compressor of Cowper's 

 glands. 



