forming cells (osteoblasts) arrange themselves along the thick bundles of fibrous tissue which radiate from the center of the future bone; by the deposition of lime-salts in these osteoblasts the deposit of bone shoots out in needle-like rays toward the circumference. (2) A deposit of bone begins at one spot of the cartilage, the primary center. The shaft is formed from this. Just before ossification commences the cartilagecells enlarge and arrange themselves in rows. Lime-salts are deposited in the matrix between the rows, forming columns which enclose oblong spaces containing cartilage-cells, called the primary areola. Now ossification proper commences by the ingrowth from the periosteum of buds of young connective tissue covered with bone-forming cells, which, after causing absorption of the cartilage, become converted into bone.

Of how many bones is the adult human skeleton composed? Two hundred, including the os hyoides, but excluding the teeth, Wormian bones, all sesamoid bones except the patellæ, and the ossicles of the middle ear.

Into what classes are bones divided?

Long bones, as femur, tibia, etc., about 90 in number; flat, as those of the vault of the skull, scapula, ribs, patella, about 40; irregular, as the vertebræ, usually symmetrical, about 40; and short, such as the carpal and tarsal bones, numbering 30.

What are Wormian bones?

Irregular fragments, developed from supplementary centers, situated at the junction of two or more cranial sutures, where, during infancy, a membranous interval existed, viz., a fontanelle. From their triangular form they are often called ossa triquetra.

What are sesamoid bones?

Those developed in the substance of tendons, whereby the muscles obtain additional leverage-i. e. power; the patella and pisiform are 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) centers of

ossification; they serve as supports and levers for power and progression.

Where are short and flat bones employed, and why?

In the carpus and tarsus, where strength with limited motion is required. The flat bones consist of two layers of compact tissue with interposed cancellous tissue, called diploë; they serve for protection and muscular attachment.

What facts are noted concerning the medullary arteries? 1. Medullary arteries run from the knee and toward the elbow. 2. The secondary center from which the artery runs is the first to appear. 3. The epiphysis first to appear is last to

unite.

How are bony prominences and cavities named?

Each variety offers an articular and a non-articular division.

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.

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

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

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 center of ossification, commonly used, however, for any process, even if an epiphysis, after it has coössified with the mass of the bone. Certain descriptive terms are used: azygos, without a fellow; coracoid, like a crow's beak; mastoid, like a nipple; rostrum, a beak; styloid, pen-like; squamous, like a scale; vaginal, ensheathing; clinoid, like a bed. 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 c-shaped, resembling the old Greek letter for s

What are the principal non-articular cavities called?

Fossæ, shallow depressions; sinuses, 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.

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 center, 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 centers 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.

BONES OF THE HEAD.

Name the bones composing the skull.

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 lacrimal, two palatal, two inferior turbinated, one vomer, and one inferior maxillary, or mandible; the ethmoid of the cranium also enters largely into the formation of the nasal cavities.

The Frontal Bone.

Of what parts does this bone consist?

Of a vertical and a horizontal portion, meeting at an angle of 60°.

Describe the points on the outer surface of the vertical portion (Fig. 1).

On each side of the median line are two frontal eminences, between which are the remains of, or the obliterated (metopic) frontal suture, leaving a slight linear depression, which, above the root of the nose, terminates in a rounded, projecting nasal

eminence (glabella). Extending from this on each side are two curved, rounded superciliary ridges, situated behind which, between the two tables of the skull, lie the frontal sinuses (Fig. 2). The junction of the vertical and horizontal portions forms on each side a curved margin, the supra-orbital arch, notched or perforated toward its inner part by the supra-orbital notch, or foramen, transmitting the artery and nerve of the same Each orbital margin terminates by two stout processes, called internal angular and external angular processes. Between the two inner projects the nasal process, in the rough, uneven space, called the nasal notch; the under surface of the nasal process presents a median ridge, nasal spine, between two

name.

grooves. The margin of the external angular process extends upward as the inferior temporal ridge (Fig. 1). Describe the points on the cerebral surface.

In the median line a frontal sulcus (Fig. 2) (for the longitudinal sinus) exists, whose edges coalesce below to form the

frontal crest, which terminates as a notch, or perhaps complete foramen cæcum (blind), which when pervious transmits a small vein.

Describe the horizontal portion.

This consists of two orbital plates of a triangular outline, separated by a quadrilateral ethmoidal notch (for articulation with the ethmoid). A shallow lacrimal fossa (for the gland) exists at the outer part of the orbit, also a trochlear fossa or sometimes a small tubercle 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