whilst towards its termination Cowper's glands are placed behind it-one on each side. The relation of the membranous part of the urethra to the triangular ligament and the parietal pelvic fascia is very important. As it emerges from the prostate, the parietal pelvic fascia (¿.e. the superior layer of the triangular ligament) sweeps backwards upon it to take part in the formation of the prostatic capsule. At its termination it pierces the triangular ligament proper about an inch below the symphysis pubis. It may therefore be looked upon as lying in the interval between these membranes. Immediately subjacent to the mucous membrane the membranous part of the urethra is surrounded by a thin coating of erectile tissue, outside which there is a muscular tunic composed of involuntary fibres arranged circularly. The Spongy Portion of the Urethra. This is the longest division of the urethra. It is embedded throughout in the substance of the corpus spongiosum penis, and shows considerable differences in its calibre as it is followed forwards to the glans. At each expansion of the corpus spongiosum there is a corresponding dilatation of the urethra. Thus the canal presents two dilatations—(1) in the bulb, and (2) in the glans; between these it is of uniform diameter, and slightly wider than the membranous part. The dilatation of the urethra in the glans is termed the fossa navicularis. At its orifice, which is termed the meatus urinarius, the canal is much contracted, and is even narrower, than any part of the membranous portion. This aperture is a vertical slit, the lower end of which is connected with the prepuce by a fold of mucous membrane, termed the frænum preputii. In the bulb and in the glans penis the erectile tissue of the corpus spongiosum is disposed very unequally around the urethra. In the former it is chiefly massed below or behind the tube, whilst in the glans it is chiefly placed in front and upon each side, a very thin layer covering it posteriorly. The ducts of Cowper's glands open into the spongy portion of the urethra by piercing its floor about an inch in front of the triangular ligament. These orifices are extremely minute, and very difficult to find. By making a small hole in the wall of the duct as it emerges from the gland, and passing a fine bristle along it, the dissector may be able to detect the opening in the urethral floor. He will notice that the ducts proceed in the first place through the erectile tissue of the bulb, but towards their termination they lie immediately subjacent to the mucous membrane. The walls of the urethra are always in apposition except when urine is flowing through it. A transverse section through the spongy portion, except at its anterior part, would give the appearance of a transverse slit. In the fossa navicularis, however, the slit becomes vertical. Mucous Membrane of the Urethra.—The mucous lining of the urethra is continuous posteriorly with that of the bladder, and anteriorly with the integument covering the glans penis. It is likewise continuous with the mucous membrane which lines the various ducts which open into the urethra. It is everywhere studded with the mouths of minute recesses, called lacunæ. These are particularly plentiful on the floor of the spongy part, and, as a general rule, they are directed forwards towards the meatus urinarius. One recess, specially deserving the attention of the student on account of its large size, is called the lacuna magna; it is placed on the roof of the fossa navicularis. Its orifice in rare cases is large enough to admit the point of a small bougie or catheter. Direction of the Urethral Canal.-The prostatic portion is directed downwards and very slightly forwards; the membranous part describes a slight curve behind the symphysis, the concavity of which looks forwards; whilst the spongy part at first ascends, and then curves downwards. The urethra, therefore, in the flaccid condition of the penis, takes a course in which there are two curves, like the letter reversed. In the erect condition of the penis the curve in the spongy part of the canal is obliterated, and there is now only one curve, the concavity of which is directed upwards. Structure of the Prostate. In the course of an ordinary dissection it is hardly to be expected that the dissector will be able to make out the structure of the prostate in all its details. It is mainly composed of involuntary muscular tissue, which is so arranged that it exercises a powerful sphincter action on the first part of the urethra. This tissue forms a layer on the outside of the organ, and also gives a coating to the urethra as it traverses the prostate. The outside and inside fibres are continuous in front-indeed, the greater part of the anterior portion of the prostate is muscular. The fibres surrounding the urethra are also continuous above with the circular fibres of the bladder, and below with the circular fibres of the membranous part of the urethra; further, they radiate out transversely into each lateral lobe. The glandular substance is interspersed amidst the muscular tissue, but none is to be seen in front of the urethra. masses. Structure of the Penis.-In the dissection of the urethra the corpora cavernosa penis have been separated from each other. Each will be seen to be enveloped in an exceedingly strong fibro-elastic sheath. In the mesial plane the sheaths become continuous with a strong septum, which intervenes between the two cylindrical This septum receives the name of septum pectiniforme, because in front it is very imperfect, being broken up by vertical slits into a series of processes like the teeth of a comb. The two fibrous cases thus constructed are filled with erectile tissue. Fibrous lamellæ and bands proceed from the deep surface of each sheath and join with each other to form a spongy framework. The interstices of this framework freely communicate with each other, and are filled with venous blood. By taking the penis to the tap and washing out the blood some idea of the trabeculæ may be obtained. The corpus spongiosum has a similar structure. The enclosing sheath, however, is very delicate, and the trabeculæ are much finer. Vesiculæ Seminales.-If the dissector has not already unravelled the vesiculæ seminales, he should now do so, and, at the same time, endeavour to make out the composition of their walls. This can best be done under water. In addition to the recto-vesical fascia which ensheathes them, each vesicula has a strong dense fibrous tunic and a certain proportion of transverse and longitudinal non-striated muscular fibres. Open them up and expose the mucous lining. remarkable for its honeycomb or reticular appearance. In this respect, This is therefore, it is not unlike the mucous membrane of the gall-bladder, only the meshes are finer and the pits smaller. PELVIC ARTICULATIONS. The pelvis is attached to the last lumbar vertebra, and its several parts are held together by the following articulations (1) Lumbo-sacral; (2) Sacro-coccygeal; (3) Coccygeal; (4) Sacro-iliac; (5) Pubic. Dissection. The nerves and blood-vessels of the pelvis must now be removed, and all adhering portions of muscle detached from the left innominate bone and the front and back of the sacrum. When this is done, the pelvis should be soaked for some time in warm water. By this proceeding the dissection of the ligaments will be rendered much easier. Lumbo-sacral Articulations. The last lumbar vertebra is joined to the sacrum by one amphiarthrodial joint, which connects the body of the vertebra to the base of the sacrum, and by two diarthrodial joints, between the two pairs of articular processes. Capsular ligaments (capsulæ articulares) surround the articulations formed by the apposition of the articular processes, and each is lined by a synovial membrane. The anterior common ligament (ligamentum longitudinale anterius) of the vertebral column is continued downwards over the anterior aspect of the body of the last lumbar vertebra to the anterior aspect of the first segment of the sacrum. In a similar manner the posterior common ligament (ligamentum longitudinale posterius) is prolonged downwards within the spinal canal, over the posterior aspect of the body of the last lumbar vertebra, to the upper part of that portion of the sacrum which forms the anterior wall of the sacral canal. Ligamenta subflava (ligamenta flava) are also present. These are two short bands of yellow elastic tissue placed one on each side of the mesial plane. Superiorly they are attached to the anterior aspect of the lower borders of the laminæ of the last lumbar vertebra; whilst inferiorly they are fixed to the posterior aspect of the upper margins of the laminæ of the first sacral segment. An interspinous ligament (ligamentum interspinale) connects the lower border of the spinous process of the last lumbar vertebra with the upper border of the spinous process of the first sacral vertebra. A supraspinous ligament (ligamentum supraspinale) bridges across between the extremities of the same spinous processes. So far, then, the ligaments of the lumbo-sacral articulations are identical with those which, above the level of the sacrum, bind the several segments of the spinal column together. Two additional ligaments - viz. the lumbosacral and the ilio-lumbar, must now be examined. The lumbo-sacral ligament is the representative of the superior costo-transverse ligaments. It is a strong triangular fibrous band attached by its apex to the tip and lower border of the transverse process of the last lumbar vertebra. Expanding as it proceeds downwards, it is fixed below to the posterior part of the base of the sacrum, where some of its fibres intermingle with those of the sacro-iliac ligaments. The ilio-lumbar ligament (ligamentum iliolumbale) may be considered to be a thickened and specially developed part of the anterior lamella of the lumbar fascia. in the same plane and is directly continuous with it. It lies |