What are sesamoid bones ?

Those developed in the substance of tendons, whereby the muscles obtain additional leverage-i. e., power; the patella are, by some, classed with these bones.

Of what parts do long bones consist, and what are their uses ?

Of a shaft (body diaphysis), two articular extremities, and various processes; they are developed in cartilage, from one principal, and one or more additional (epiphyseal) centres of ossification; they serve as supports and levers for power and progression. Where are short bones employed, and why?

In the carpus and tarsus, where strength with limited motion is required. They ossify in cartilage.

Describe the structure and uses of flat bones.

They consist of two layers of compact tissue with interposed cancellous tissue, called diploë; they serve to protect important viscera, as brain, etc., and afford extended surfaces for origin of muscles; for the most part, they ossify in membrane.

How are bony prominences named?

Processes, and are described as articular and non-articular.

Give the names and characteristics of the chief articular processes.

Head, a convex smooth projection, with a constriction or neck beneath; found in freely moving joints.

3 Condyles, double projecting processes, may have a constriction or neck-i. e., neck of condyle of jaw.

Trochanters, short projecting levers near articulations to facilitate rotation of the bone on its long axis.

Tuberosities, roughened, broad prominences.

Tubercles, similar to the above, but small with reference to the size of the bone.

Spines and spinous processes, more or less pointed projections. Apophysis, strictly speaking, any bony process which develops from the primary centre of ossification, commonly used, however,

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for any process, even if an epiphysis, after it has coössified with the mass of the bone.

What is a diaphysis?

The main portion of a bone (shaft in a long bone, body in an irregular one) between the epiphyses.

What is an epiphysis?

A supplementary centre, usually to provide for growth in length, developed in cartilage, which remains separated by a layer of epiphyseal cartilage until the growth of the bone is completed, when it coössifies with the diaphysis, and all further growth ceases. Epiphyseal centres appear after birth: they coössify in the inverse order of their appearance, except that of the lower end of the fibula. This process of coössification commences about puberty, and the last to unite are those of the upper end of the tibia and the vertebral bodies-as late as twenty-five years.

Mention some of the non-articular processes, with their meaning.

Azygog, without a fellow; coronoid, or coracoid, like a crow's beak; mastoid, like a nipple; rostrum, a beak; styloid, pen-like; squamous, scaly; vaginal, ensheathing.

Name some of the articular cavities of bone.

Cotyloid, when they resemble a deep cup glenoid, when they have a shallow-cup form; trochlear, pulley-like facet, when smooth, like one of the surfaces of a cut gem; sigmoid, when

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What are the principal non-articular cavities called?

Fosse, shallow depressionsinuses, deep cavities, communicating with the exterior by small openings; grooves, long narrow depressions; fissures, cracks; notches, deficiencies of edges of bones; foramina, holes through bones for transmission of nerves, etc.

BONES OF THE HEAD.

Name the bones composing the head.

They are twenty-two in number: eight of which (cranial) compose the brain-case, viz., one frontal, two parietal, two temporal, one sphenoid, one occipital, and one ethmoid; fourteen are facial: two superior maxillary, two malar, two nasal, two lachrymal, two palate, two inferior turbinated, one vomer, and one inferior maxillary; the ethmoid also enters largely into the formation of the nasal cavities.

The Frontal Bone.

Of what parts does this bone consist?
Of a vertical and horizontal portion.

FIG. 1.

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Describe the points on the outer surface of the vertical portion.

On each side of the median line are two frontal eminences1, between which are the remains of, or the completely obliterated, inter-frontal suture, leaving a slight linear depression, which, above the root of

the nose, terminates in a rounded, projecting nasal eminence. Extending outward from this on each side are two curved, rounded superciliary ridges, situated beneath which, between the two tables of the skull, lie the frontal sinuses1 (Fig. 2). The junction of the vertical and horizontal portions forms on each side a curved margin, the supra orbital arch3-4, notched or perforated toward its inner part by the supra-orbital notch, or foramen, transmitting the artery, vein, and nerve of the same name. Each orbital margin terminates by two stout processes, called internal angular and external angular processes. Between the inner projects the nasal spine, in the rough, uneven space, called the nasal notch; the margin of the external angular process extends upward as a temporal ridges (Fig. 1).

Describe the points on the inner surface.

In the median line a vertical groovelo (Fig. 2) (for the longitudinal sinus) exists, whose edges coalesce below to form the frontal crest11, which terminates as a notch, or perhaps complete foramen cacum13, which when pervious transmits a small vein.

that bone). A shallow lachrymal 12 depression (for gland) exists at the outer part of the orbit, also a smaller one or sometimes a small tubercle15 at the anterior inner part for the pulley of the superior oblique muscle. Several half cells are seen along the margins of the ethmoidal notch, which complete the ethmoidal cells when the ethmoid is in position, as well as two grooves, which are likewise converted into the anterior and posterior ethmoidal canals, the former for the nasal nerve and anterior ethmoidal vessels, the latter for the posterior ethmoidal vessels. On each side of the nasal spine open the frontal sinuses1 (absent in children), a part of the nasal cavities, into which they open by the infundibulum. The inner surfaces of both vertical and horizontal portions present numerous depressions for the convolutions of the brain, and branching grooves for the anterior meningeal artery.

What centres of ossification has this bone?

Two, near the orbital arches, in membrane, seventh or eighth fœtal week.

With what bones does it articulate ?

With two parietal, the sphenoid, the ethmoid, two nasal, two superior maxillary, two lachrymal, and two malar-twelve in all. What muscles arise from it?

The corrugator supercilii, orbicularis palpebrarum, and temporal, on each side.

Parietal Bones.

Describe a parietal bone.

It is of a quadrilateral form, convex externally, the most prominent point called the parietal eminence. Its upper serrated border forms with its fellow the sagittal suture1; the anterior serrated margin articulates with the frontal, forming part of the coronal sutures; its anterior inferior angle', more prolonged than the others, articulates inferiorly with the sphenoid (spheno-parietal suture); the remainder of the inferior border2, bevel-edged, is overlapped by the squamous plate of the temporal (squamo-parietal suture); the posterior serrated border1 articulates with the occipital (occipito-parietal part of lambdoid suture); while the posterior