eminence20 indicates the point of junction with the ilium; the inner end is the oval symphysis11 with eight or nine ridges for attachment of the fibro-cartilage; the upper triangular surface presents posteriorly the pectineal portion of the ilio-pectineal linel; the anterior surface presents the crest, ending externally in the pubic spinel giving attachment to Poupart's ligament, internally in the angle; below is a groove for the obturator vessels and nerve; the descending ramus13, thin and flat, joins that of the ischium, completing the anterior boundary of the obturator foramen.

How are these bones developed ?

By three primary centres, one for each bone (from the eighth foetal week to fifth foetal month); and one for the crest, one for the tuberosity, one for the anterior inferior spine, one for symphysis, and one Y-shaped, joining the three pieces forming the acetabulum, appearing about puberty; bone coössifies completely about 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, pelvic floor and rotators of the thigh.

Describe the sacrum.

It is composed of five consolidated vertebræ, is of triangular form with broad base and blunted apex and lateral expanded masses or alæ; its anterior surface is concave, its posterior convex, and with the coccyx it forms the posterior wall of the true pelvis. Its anterior surface is marked by four transverse ridges1, indicating the lines of junction of the segments; eight anterior sacral foramina2 with broad shallow grooves for the anterior sacral nerves open on this surface; the point of junction with the last lumbar vertebra forms the promontory (sacro-vertebral angle); and upon each side are the ala-the expanded portions of the bone. Posteriorly are three or four median tubercles (rudimentary spinous processes); externally are the lamina, those of the fifth and sometimes the fourth being deficient; outside these is a row of rudimentary articular processes. On each side of the spine is a broad sacral groove, lodging the origin of the erector spine muscle; externally are the four posterior sacral foramina on each

side; at the posterior inferior portion of the bone are the two cornua-articulating surfaces for the coccyx; each lateral surface

has on its anterior upper part an auricular surface for articulation with the ilium; on each side of the apex below is a deep notch,10 11, for the fifth sacral nerve; the base resembles the upper surface of a lumbar vertebra, with the last of which it articulates; the apex, directed downward and forward, has an oval concave articular surface for the coccyx; the sacral canal runs the whole length of the bone, triangular above, small and flattened below. and deficient in its posterior wall at the lower part; it lodges the sacral nerves, and into it open the anterior and posterior sacral foramina.

What centres of ossification has the sacrum?

Thirty-five, appearing from the eighth foetal week to the twentieth year, coössification being complete from the twenty-fifth to thirtieth year. The bodies have each three centres; each lamina one centre; the lateral masses three centres each; the lateral surfaces two each.

Give the muscular attachments.

The pyriformis, coccygeus and iliacus in front, the gluteus maximus, latissimus dorsi, multifidus spinæ, erector spinæ, and sometimes the extensor coccygis behind.

Describe the coccyx.

Usually composed of four rudimentary vertebræ, more or less coössified, it forms a triangular bone whose base articulates with

the sacral apex. The first piece presents two cornua2, projecting upward from either side of the base for articulation with the sacral cornua, their junction completing the fifth sacral foramina for the posterior branches of the fifth nerves. The apex is rounded and occasionally bifid or turned to one side; two rudimentary transverse processes3 are seen on the first piece.

Describe its development.

From four centres: one for each segment, the first piece commencing at birth; second, five to ten years; third, ten to fifteen years; fourth, fifteen to twenty years; coössification varies as to time and manner.

Give the muscular attachments.

Laterally the coccygei; behind the gluteus maximus and extensor coccygeus (when present); apex, sphincter ani; in front levator ani.

Describe the pelvis.

The Pelvis.

Formed by the two innominate bones, the sacrum and the coccyx, all above the ilio-pectineal line 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 oy the linea ilio-pectinea at the sides, completed in front by the spine and

FIG. 32.

crest of the pubes, behind by the anterior margin of the base of the sacrum and promontory of the sacrum. Its average diameters in the female are, antero-posteriord, four and one-half inches; transversetr, five and a quarter inches; the oblique, 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, quadrangular inner surface of the body of the ischium, forming a curved canal wider in the middle than at its outlets, measuring in depth at the symphysis one and one-half inches, three and one-half inches in the middle axial line, and four and onehalf 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 tuberosities of the ischium, the pubic arch in front and tip of the coccyx behind. Its diameters are four and one-quarter to four and threequarters inches transverse, antero-posterior and oblique four and one-half increased to five by pressure on the coccyx; in the male, the diameters average three and one-half inches.

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

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 f, its outer third flattened from above downward, and concave anteriorly; the inner two-thirds are cylindrical and convex anteriorly, and it extends

FIG 33.

A 2

B

almost horizontally between the sternum and scapula, the two extremities being respectively termed the sternal1 and acromial2. Describe the chief points presented by the clavicle, commencing at the outer extremity.

The upper surface has impressions, that in front for the deltoid," that behind for the trapezius; at the outer end is a facet articulating with the acromium process of the scapula; at the posterior border, beneath, is the conoid tubercle, just above the coracoid process of scapula, for the conoid ligament; extending from the tubercle, forward and outward, nearly to the outer end of the anterior border is the oblique line for the trapezoid ligament; occasionally at the centre of the anterior border of the outer third is the deltoid tubercle. The under surface of the middle portion presents the subclavian groove for the same named muscle-here appears the nutrient foramen directed outward; the inner third of the superior border bears an impression for the sterno-mastoid muscle (A, Fig. 33), while the inner half of the anterior margin has another impression for the pectoralis major muscle. Beneath the posterior border of the sternal end is the rhomboid impression,5 for the rhomboid or costo-clavicular ligament. The sternal end1 is triangular in form, its inner surface for articulation with the sternum, this surface being continuous with a facet beneath, for articulation with the first costal cartilage.