different subjects, and at different periods of life. In the young subject, a thin fibro-cartilage is found between the

A POSTERIOR VIEW OF THE LIGAMENTS OF THE PELVIS.-1. Base of the Sacrum. 2. The coccyx. 3, 3. The crests of the ilia. 4, 4. The tuberosities of the ischia. 5, 5. The great sciatic notches. 6. The small sciatic notch. 7. The femur. 8, 8. The posterior sacro-iliac ligaments. 9. An oblique fasciculus. 10. The posterior sacro-coccygeal ligament. 11. The obturator ligament. 12. The sub-pubic foramen. 13, 13. The origin of the great sacro-sciatic ligament. 14. Its insertion. 15. The origin of the small sacro-sciatic ligament. 16. Its insertion.

bones, while in the old the joints are most commonly obliterated. The sacrum and coccyx are also in the old generally united by osseous substance.

The sacro-iliac articulation is formed by the sacrum and ilium. The articular surfaces, from their shape, have been called the auricular facets. The connecting media consist of anterior and posterior fibres, and an intermediate layer of cartilage, which adheres very closely to the bones.

The ANTERIOR SACRO-ILIAC LIGAMENT, Fig. 233 (1), is composed of a thin layer of fibres, extending transversely from one bone to the other; they are scarcely raised above the contiguous smooth surfaces.

The POSTERIOR SACRO-ILIAC LIGAMENT, Fig. 232 (8), consists of several fasciculi, which extend from a rough surface behind the auricular facet of one bone to a corresponding surface on the other. Some of the fibres are oblique, and others

are nearly transverse. One or two of the oblique fasciculi, Fig. 232 (9), have been described as distinct ligaments. The ligament is situated deeply in the groove formed between the sacrum and ilium; it requires considerable time and patience to make a satisfactory exposition of all its fibres or fasciculi. A synovial membrane is sometimes found in this articulation, especially in the female, while a soft yellowish substance is sometimes met within it in the male. As it is occasionally desirable to disarticulate the os innominatum, as in making a dissection of the pelvic viscera, the student should be careful to ascertain the exact position of the symphysis, in front, and divide all the fibres of the anterior ligament, when a small scalpel can be carried through the cartilage which connects the two bones forming the joint.

The two following ligaments connect the sacrum and coccyx to the ischium. They enter so largely into the formation of the pelvic parietes, and sustain such important relations to various parts, that the student cannot neglect to obtain a thorough knowledge of them without doing great injustice to himself. They should be carefully studied before he attempts to make a dissection of the pelvis or the pelvic viscera. Their value in the mechanism of the pelvis will be observed the moment that he contrasts an articulated pelvis, composed simply of the bones, with one prepared with these ligaments cleaned and retained in situ.

The POSTERIOR OF GREAT SACRO-SCIATIC LIGAMENT, Fig. 233 (4), is of a somewhat triangular shape, with the base attached to the posterior inferior spinous process of the ilium and to the border of the sacrum and coccyx, and the apex to the inner edge of the tuberosity of the ischium and to the ramus of the same bone. The obturator fascia is connected to the anterior or falciform portion of this ligament, which projects a little into the perineum, and serves to protect the internal pudic vessels. The posterior surface of this ligament is occupied by the origin of a part of the gluteus maximus muscle, while the anterior surface is partly free, looking into the pelvic cavity, and partly in apposition with the short ligament. It is perforated by small foramina for the transmission of vessels.

The ANTERIOR or SMALL SACRO-SCIATIC LIGAMENT, Fig. 233 (5), is attached behind to the side of the sacrum and

coccyx, and anteriorly to the spine of the ischium. Its form is triangular, and its direction is nearly transverse. Pos

ING

Fig. 233.

A SECTION OF THE PELVIS, SHOWTHE LIGAMENTS AND SACRONER SIDE, viz: 1. Great sacro-sciatic foramen. 2. Small sacro-sciatic fora3. Sacro-coccygean ligament.

SCIATIC FORAMINA ON THE LEFT IN

men.

4. Great sacro-sciatic. 5. Sinall sa

cro-sciatic. 6. Symphysis pubis. 7. Anterior sacro-iliac ligament. 10.

Obturator.

teriorly, it is covered principally by the great ligament, with which its fibres are more or less intermingled, especially at its base or near the sacrum. Anteriorly, it is in apposition with the coccygeus muscle.

The great and small sacrosciatic notches, which exist in the osseous pelvis, are by these two ligaments converted into the great and small sacro-sciatic foramina, Fig. 233 (1,2). As the spine of the ischium separates the two notches, so the small sacro-sciatic ligament separates the two foramina. The contents of these foramina require particular notice in the dissection of the parts inside of the pelvis and in the gluteal region.

The articulation formed by the bodies of the pubic bones is designated the symphysis pubis, Fig. 233 (6). The space between these bones is of a cuneiform shape, the base looking forwards and downwards, and the thin edge backwards and upwards. This space is filled with fibro-cartilage, including sometimes an imperfect synovial sac, especially in the female. The fibro-cartilage is arranged in concentric layers of an elongated oval form; short fibres penetrate and connect them together, except in the centre and posteriorly, where a soft pulpy substance is found, or the synovial sac when present. As the lamina just fill the circumference of the space between the bones, they are thicker or more numerous in front than behind, where they project so as to form a vertical ridge; some of them may be entirely deficient behind.

Surrounding this intermediate structure, ligamentous fibres extend from one bone to the other. They are named according to their location. Thus, we have quite a thick, strong fasciculus of fibres above, passing from one bone to the other and continuing some distance on their upper borders; this

is named the superior pubic ligament. Behind, there are fibres which connect the two bones together; they do not form, however, so thick a layer as the upper and anterior ones do; they constitute the posterior pubic ligament. Anteriorly, there is also the same arrangement of fibres, forming the anterior pubic ligament. Below, the fibres interlace, and extend downwards on the rami of the pubes, and form the sub-pubic ligament, which is of a triangular shape. This ligament rounds off the angle formed by the rami of the pubic bones, and forms the summit of the pubic arch. The symphysis pubis is supposed by some to allow of a slight degree of mobility in parturition. If motion takes place at all, it must be so little as to produce scarcely any appreciable effect in increasing the diameters of the pelvis.

The OBTURATOR LIGAMENT or MEMBRANE, Fig. 233 (10), occupies the obturator foramen. It presents an opening called the sub-pubic foramen, Fig. 232 (12), in the upper part, corresponding to the sub-pubic groove in the horizontal ramus of the os pubis, for the transmission of the obturator nerve and vessels. Its surfaces are occupied by the origins of the obturator muscles. This fibrous membrane is a substitute for osseous structure in the parietes of the pelvis, which are probably rather strengthened than weakened by it; it may also yield somewhat in parturition, and thus facilitate the passage of the head of the child through the pelvis. Another advantage said to be derived from it, is that it is lighter than bone would be; the difference, however, between its weight and that of a thin lamella of bone could make no manifest difference.

Poupart's and Gimbernat's ligaments, Fig. 220 (6,7), are formed by the lower border of the tendon of the external oblique muscle, with the addition of some fibres which arise from the anterior superior spinous process of the ilium; they are noticed in the dissection both of that muscle and of the femoral region.

SECT. III.-DISSECTION OF THE BACK OF THE THIGH, AND OF THE HAM.

The back part of the thigh and the popliteal space should be examined at the same time, commencing the dissection above, and extending it down as far as the back of the

leg. With a little attention, the student will be able to ascertain the best position in which to place the limb as he proceeds with the dissection. To expose the long muscles on the back of the thigh, the leg should be extended on the thigh, and the thigh flexed on the pelvis. To remove the skin, an incision may be made through it in the median line of the limb, beginning at the gluteal region and terminating about three or four inches below the knee-joint; but if the anterior part of the thigh has already been dissected, the integument may be removed, by simply reflecting it either from the inner or the outer part of the limb. The superficial fascia in these regions is merely a continuation of the superficial fascia from the fore part of the thigh and the pelvis. There are no arteries that require any particular notice in this fascia; and the only vein of sufficient importance, and which was not seen in the dissection of the anterior part of the thigh, to be particularly noticed, is the external saphenous.

Fig. 234.

The external or short saphenous vein is a continuation of the external dorsal vein of the foot. It will be found, in this dissection, extending up the back part of the leg in the median line, and entering the popliteal space to open into the popliteal vein. Sometimes quite a large venous trunk is found going from this vein to the upper part of the thigh, where it unites with a branch of the internal saphenous, or of the deep femoral vein.

The cutaneous nerves, Fig. 234 (2, 2), on the back part of the thigh and in the ham are derived, on the inner side, from the internal cutaneous, and from the internal saphenous, or the obturator nerve; on the outer side, from the external cutaneous; and in the middle, from the posterior femoral cutaneous.

PLAN OF THE CUTANEOUS NERVES ON THE POSTERIOR ASPECT OF THE LEFT LEG.1. Inner division of the internal cutaneous nerve. 2, 2. Branches of the long or internal saphenous. 3. A branch of the posterior femoral cutaneous; the offset above it in a direct line is a branch of the same nerve. 4, 6. Short or external săphenous nerve. 5, 7. Peroneal cutaneous nerve.