a large ovoidal opening in the male, a smaller and triangular one in the female.

Describe the ilium.

This is the upper expanded portion of the bone (Fig. 51), presenting along its upper border the crest with its outer and inner lips, terminating in front by the anterior superior spinous process, giving origin to Poupart's ligament, the sartorius and tensor fasciæ femoris muscles, and behind by the posterior superior spinous process, to which are attached part of the erector spinæ muscle and the oblique band of the sacroiliac ligament. Below both the anterior and posterior spines is a process called, respectively, the anterior (for the straight tendon of the rectus femoris muscle) and posterior inferior spinous (for the great sacro-sciatic ligament); by these projections a notch is formed in front and behind, the former giving partial origin to the sartorius muscle and transmitting the external cutaneous nerve. Between the posterior inferior spine and the spine of the ischium is situated the greater sacro-sciatic notch, giving exit to the pyriformis muscle, the greater and lesser sciatic, superior and inferior gluteal and pudic nerves, also one to the obturator internus muscle, and the sciatic, gluteal, and pudic vessels. About two inches from the posterior superior spine, passing downward and outward from the crest, is the superior gluteal line, from the surface back of which arise the gluteus maximus muscle and a few fibers of the pyriformis; about an inch behind the anterior superior spine, passing from the crest downward and backward to the upper part of the great sacro-sciatic notch, is the middle gluteal line, the gluteus medius arising from the space between these two lines; passing downward and backward, from the upper part of the anterior inferior spine to the front of the sacro-sciatic notch, is the inferior gluteal line, between which and the middle arises the gluteus minimus. Above the acetabulum is a groove for the reflected tendon of the rectus femoris muscle. The inner surface presents (Fig. 52) in front the iliac fossa for the iliacus muscle and a broad groove for the psoas-iliacus tendon; posteriorly is seen-1, a smooth surface below the ilio-pectineal line in the true pelvic cavity; 2, an auricular surface for the sacrum; 3, a rough surface for the sacro-iliac ligaments; 4, a rough surface for the muscles of the back.

Describe the ischium.

It consists of a body, tuberosity, and ramus, and forms the lowest part of the innominate bone. The external surface of the body forms two-sixths of the acetabulum; below this is a

FIG. 52.-Right os innominatum, internal surface (Gray).

groove for the obturator externus tendon; its inner surface forms the lateral boundary of the true pelvis; from the posterior border, below the center, projects the spine of the ischium, above and below which are the greater and lesser sacro-sciatic notches, the latter giving egress to the obturator internus muscle and ingress to its nerve and to the pudic vessels and nerve. The lowest portion presents a tuberosity, with an outer and an

inner lip to the latter being attached the greater sacro-sciatic ligament; to the outer is attached the quadratus femoris and adductor magnus muscles. Passing upward and inward from the tuberosity to join the ramus of the pubes, and bounding the obturator foramen in front, is the thin, flattened ascending

ramus.

Describe the pubes.

This bone (also called pectineal) consists of a body, a horizontal and a descending ramus. The outer end of the horizontal ramus forms one-sixth of the acetabulum; above, a rough liopectineal eminence indicates the point of junction with the ilium; the inner end is the oval symphysis with eight or nine ridges for attachment of the fibro-cartilage; the upper triangu

FIG. 53.-Plan of the development of the os innominatum.

lar surface presents posteriorly the pectineal portion of the iliopectineal line; the anterior surface presents the crest, ending externally in the pubic spine giving attachment to Poupart's ligament, internally in the angle; below is a groove for the

obturator vessels and nerve; the descending ramus, thin and flat, joins that of the ischium, completing the anterior boundary of the obturator foramen.

How are these bones developed?

By three primary centers (Fig. 53), one for each bone (from the eighth fetal week); and five secondary centers: one for the crest, one for the tuberosity, one for the anterior inferior spine, one for the symphysis, and one Y-shaped, joining the three pieces forming the acetabulum, appearing about puberty; bone coössifies completely about the twenty-fifth year. (For order of junction, see Gray.)

What muscular attachments has the innominate bone? Those of the abdomen, some of the thigh, those of the perineum and pelvic floor.

Describe the pelvis.

The Pelvis.

Formed by the two innominate bones, the sacrum and the соссух, coccyx, all above the ilio-pectineal lines is called the false pelvis, consisting of the two iliac fossa; all below, the true pelvis.

Describe the true pelvis.

Its brim, or inlet, somewhat heart-shaped, is formed by the linea ilio-pectinea at the sides, completed in front by the spine

FIG. 54.-Diameters of the pelvis.

and crest of the pubes, behind by the anterior margin of the base of the sacrum and promontory of the sacrum.

Its aver

age diameters in the female are, antero-posterior", four inches; the oblique, four and one-half inches; transverse", five inches; its long axis, if extended, would pass from the middle of the coccyx to the umbilicus; in the male these measurements are diminished by at least one-half inch.

Describe the cavity.

This is bounded in front by the symphysis pubis, behind by the concavity of the sacrum and coccyx, on either side by the broad, smooth inner surface of the ischium and by the lower part of the ilium, forming a curved canal wider in the middle than at its outlets, measuring in depth of the symphysis one and one-half inches, three and one-half inches in the middle axial line, and four and one-half inches posteriorly, perhaps as much as five and one-half inches in males.

Describe the lower circumference of the pelvis.

This is called the outlet, is bounded on each side by the tuberosity of the ischium, the pubic arch in front and tip of the coccyx behind. Its diameters, antero-posterior, oblique, and transverse, measure respectively five, four and one-half, and four inches, being the reverse of the diameters of the inlet, explaining the rotation of the fetal head; in the male the diameters average three and one-half inches.

What are the chief differences between the male and the female pelvis ?

The strength of the bones, distinctness of the muscular impressions, the depth and narrowness of the cavity, and large obturator foramina mark the male pelvis; the lighter bones, broader iliac fossæ, the less-curved sacrum, the wider pubic arch, and the universally greater diameters distinguish the female pelvis.

BONES OF THE UPPER EXTREMITY.

Name the bones.

The clavicle, scapula, humerus, radius, ulna, scaphoid, semilunar, cuneiform, pisiform, trapezium, trapezoid, os magnum, unciform, five metacarpal, and fourteen phalangeal bones. Describe the clavicle.

It is a long bone, curved like the italic letter ƒ, its outer third