THE UPPER EXTREMITY
THE ULNA
The Ulna is a long bone, prismatic in form, placed at the inner side of the fore-arm, parallel with the radius, being the largest and longest of the two. Its upper extremity, of great thickness and strength, forms a large part of the articulation of the elbow joint; it gradually tapers as it descends, its inferior extremity being very small, and excluded from the wrist joint by the interposition of an interarticular fibro-cartilage. It is divisible into a shaft and two extremities.
The Upper Extremity, the strongest part of the bone, presents for examination two large curved processes, the Olecranon process and the Coronoid process, and two concave articular cavities, the greater and lesser Sigmoid cavities.
The Olecranon Process is a large thick curved eminence, situated at the upper and back part of the ulna. It rises somewhat higher than the coronoid, is contracted where it joins the shaft, and curved forwards at the summit so as to present a prominent tip. Its posterior surface, directed backwards, is of a triangular form, smooth, subcutaneous, and covered by a bursa. Its superior surface, directed upwards, is of a quadrilateral form, marked behind by a rough surface for the attachment of the Triceps muscle, and in front, near the margin, by a slight transverse groove for the attachment of part of the posterior ligament of the elbow joint. Its anterior surface is smooth, concave, covered with cartilage in the recent state, and forms the upper and back part of the great sigmoid cavity. The lateral borders present a continuation of the same groove that was seen on the margin of the superior surface, they serve for the attachment of ligaments, viz., the back part of the internal lateral ligament internally; the posterior ligament externally. The Olecranon process, in its structure as well as in its position and use, resembles the Patella in the lower limb, and, like it, sometimes exists as a separate piece, not united to the rest of the bone.
The Coronoid Process (icopcavi), a crow's beak; etSo?) is a rough triangular eminence of bone which projects horizontally forwards from the upper and front part of the ulna, forming the lower part of the great sigmoid cavity. Its base is continuous with the shaft. Its apex, pointed, slightly curved upwards, is received into the coronoid depression of the humerus in flexion of the fore-arm. Its superior surface is smooth, concave, and forms the lower part of the great sigmoid cavity. The inferior surface is concave, directed downwards and forwards and marked internally by a rough impression for the insertion of the Bra-chialis anticus. At the junction of this surface with the body, is a rough eminence, the tubercle of the ulna, for the attachment of the oblique ligament. Its outer surface presents a narrow, oblong, articular depression, the lesser sigmoid cavity. The inner surface, by its prominent free margin, serves for the attachment of the front part of the internal lateral ligament. At the front part of this surface is a small rounded eminence for the attachment of one head of the Flexor digitorum sublimis. Behind the eminence, a depression for part of the origin of the Flexor profundus digitorum, and descending from it a ridge, lost below on the inner border of the shaft, which gives attachment to one head of the Pronator radii teres.
The Greater Sigmoid Cavity , so culled from its resemblance to the Greek letter S, is a semi-lunar depression of large size, situated between the olecranon and coronoid processes, and serving for articulation with the trochlear surface of the humerus. About the middle of either lateral border of this cavity ia a notch, which contracts it somewhat, and serves to indicate the junction of the two processes of which it is formed. The cavity is concave from above downwards, and divided into two lateral parts by a smooth elevated ridge, which runs from the summit of the olecranon to the tip of the coronoid process. Of these two portions, the internal is the largest, and slightly concave transversely; the external the smallest, being nearly plane from side to side.
The Lesser Sigmoid Cavity is a narrow, oblong, articular depression, placed on the outer side of the coronoid process, and serving for articulation with the head of the radius. It is concave from before backwards; and its extremities, which are prominent, serve for the attachment of the orbicular ligament.
The Shaft is prismatic in form at its upper part, and curved from behind forwards, and from within outwards, so as to be convex behind and externally; its central part is quite straight; its lower part rounded, smooth, and bent a little outwards; it tapers gradually from above downwards, and presents for examination three borders and three surfaces.
The Fore-Arms
The anterior border commences above at the prominent inner angle of the coronoid process, and terminates below in front of the styloid process. It is well marked above, smooth and rounded in the middle of its extent, and affords attachment to the Flexor profundus digitorum, sharp and prominent in its lower fourth for the attachment of the Pronator quadratus. It separates the anterior from the internal surface.
The posterior border commences above at the apex of the triangular surface at the back part of the olecranon, and terminates below at the back part of the styloid process; it is well marked in the upper three-fourths, and gives attachment to an aponeurosis common to the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor profundus digitorum muscles; its lower fourth is smooth and rounded. This border separates the internal from the posterior surface.
The external border commences above by two lines, which converge one from each extremity of the lesser sigmoid cavity, enclosing between them a triangular space for the attachment of part of the Supinator brevis, and terminates below at the middle of the articular surface for the radius. Its two middle-fourths are very prominent, and serve for the attachment of the interosseous membrane; its lower fourth is smooth and rounded. This border separates the anterior from the posterior surface.
The Fore-Arms
The anterior surface, much broader above than below, is concave in the upper three-fourths of itd extent, and affords attachment to the Flexor profundus digitorum. Its lower fourth, also concave, to the Pronator quadratus. The lower fourth is separated from the remaining portion of the bone by a prominent ridge, directed obliquely from above downwards and inwards; this ridge marks the extent of attachment of the Pronator above. At the junction of the upper with the middle third of the bone is the nutritious canal, directed obliquely upwards and inwards.
The posterior surface, directed backwards and outwards, is broad and concave above, somewhat narrower and convex in the middle of its course, narrow, smooth, and rounded below. It presents above an oblique ridge, which runs from the posterior extremity of the lesser sigmoid cavity, downwards to the posterior border, marking off a small triangular surface above it for the insertion of the Anconeus muscle, whilst the ridge itself affords attachment to the Supinator brevis. The surface of bone below this is subdivided by a longitudinal ridge into two parts, the internal part is smooth, concave, and gives origin (occasionally is merely covered by) the Extensor carpi ulnaris. The external portion, wider and rougher, gives attachment from above downwards to part of the Supinator brevis, the Extensor ossis metacarpi pollicis, Extensor secundii internodii pollicis, and Extensor indicis muscles.
The internal surface is broad and concave above, narrow and convex below. It gives attachment by its upper three-fourths to the Flexor profundus digitorum muscle; its lower fourth is subcutaneous.
The Lower Extremity of the ulna is of small size, and excluded from the articulation of the wrist joint. It presents for examination two eminences; the outer larger is a rounded articular eminence, termed the head of the ulna. The inner, narrower and more projecting, is a non-articular eminence, the styloid process. The head presents an articular facet, part of which, of an oval form, is directed downwards, and plays on the surface of the triangular fibre-cartilage, which separates this bone from the wrist joint; the remaining portion, directed outwards, is narrow, convex, and received into the sigmoid cavity of the radius. The styloid process projects from the inner and back part of the bone, and descends a little lower than the head, terminating in a rounded summit, which affords attachment to the internal lateral ligament of the wrist. The head is separated from the styloid process below and in front, by a depression for the attachment of the triangular inter-articular fibro-cartilage; behind, by a shallow groove for the passage of the tendon of the Extensor carpi ulnaris.
Structure. Similar to that of the other long bones.
Development. By three centres; one for the shaft, one for the inferior extremity, and one for the olecranon. The centre for the shaft appears a short time after the radius, and soon extends through the greater part of the bone. At birth, the ends are cartilaginous. About the fourth year, a separate osseous nucleus appears in the middle of the head, which soon extends into the styloid process. About the tenth year, ossific matter appears in the upper cartilaginous end of the bone near its extremity, the chief part of the olecranon being formed from an extension of the shaft of the bone into it. At about the sixteenth year, the upper epiphysis becomes joined, and at about the twentieth the inferior one.
Articulations. With the humerus and radius.
Attachment of Muscles. To the olecranon; the Triceps, Anconeus, and one head of the Flexor carpi ulnaris. To the coronoid process; the Bra-chialis anticus, Pronator radii teres, Flexor sublimis digitorum, and Flexor profundus digitorum. To the shaft; the Flexor profundus digitorum, Pronator quadratus, Flexor carpi ulnaris, Extensor carpi ulnaris, Anconeus, Supinator brevis, Extensor ossis meta-carpi pollicis, Extensor secundi inter-nodii pollicis, and Extensor indicia.
The Development of Ulna
THE RADIUS
The Radius is situated on the outer side of the fore-arm, lying parallel with the ulna, which exceeds it in length and size. Its upper end is small, and forms only a small part of the elbow-joint; but its lower end is large, and forms the chief part of the wrist. It is one of the long bones, having a prismatic form, slightly curved longitudinally, and presenting for examination a shaft and two extremities.
The Upper Extremity presents a head, neck, and tuberosity. The head is of a cylindrical form, depressed on its upper surface into a shallow cup, which receives the radial or lesser head of the humerus. Around the circumference of the head is a smooth articular surface, coated with cartilage in the recent state, broad internally where it articulates with the lesser sigmoid cavity of the ulna, narrow in the rest of its circumference, to play in the orbicular ligament. The head is supported on a round, smooth, and constricted portion of bone, called the neck, which presents, behind, a slight ridge, for the attachment of part of the Supinator brevis. Beneath the neck, at the inner and front aspect of the bone, is a rough eminence, the tuberosity. Its surface is divided into two parts by a vertical line — a posterior rough portion, for the insertion of the tendon of the Biceps muscle; and an anterior smooth portion, on which a bursa is interposed between the tendon and the bone.
The Shaft of the bone is prismoid in form, narrower above than below, and slightly curved, so as to be convex outwards. It presents three surfaces, separated by three borders.
The anterior border extends from the lower part of the tuberosity above, to the anterior part of the base of the styloid process below. It separates the anterior from the external surface. Its upper third is very prominent; and, from its oblique direction downwards and outwards, has received the name of the oblique line of the radius. It affords attachment, externally, to the Supinator brevis; internally, to the Flexor longus pollicis, and between these to the Flexor digito-rum sublimis. The middle third of the anterior border is indistinct and rounded. Its lower fourth is sharp, prominent, affords attachment to the Pronator quadra-tus, and terminates in a small tubercle, into which is inserted the tendon of the Supinator longus.
The posterior border commences above, at the back part of the neck of the radius, and terminates below, at the posterior part of the base of the styloid process; it separates the posterior from the external surface. It is indistinct above and below, but well marked in the middle third of the bone.
The internal or interosseous border commences above, at the back part of the tuberosity, where it is rounded and indistinct, becomes sharp and prominent as it descends, and at its lower part bifurcates into two ridges, which descend to the anterior and posterior margins of the sigmoid cavity. This border separates the anterior from the posterior surface, and has the interosseous membrane attached to it throughout the greater part of its extent.
The anterior surface is narrow and concave for its upper two-thirds, and gives attachment to the Flexor longus pollicis muscle; below, it is broad and flat, its lower fourth giving attachment to the Pronator -quadratus. At the junction of the upper and middle thirds of this surface is the nutritious foramen, which is directed obliquely upwards.
The posterior surface is rounded, convex, and smooth in the upper third of its extent, and covered by the Supinator brevis muscle. Its middle third is broad, slightly concave, and gives attachment to the Extensor ossis metacarpi pollicis above, the Extensor primi internodii pollicis below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone.
The external surface is rounded and convex throughout its entire extent. Its upper third gives attachment to the Supinator brevis muscle. About its centre is seen a rough ridge, for the insertion of the Pronator radii teres muscle. Its lower part is narrow, and covered by the tendons of the Extensor ossis metacarpi, and Extensor primi internodii pollicis muscles.
The Lower Extremity of the radius is large, of quadrilateral form, and provided with two articular surfaces, one at the extremity, and one_at the inner side of the bone; it presents, also, three borders, an anterior, posterior, and external. The articular surface at the extremity of the bone is of triangular form, concave, smooth, and divided by a slight ridge into two parts. Of these, the external is large, of a triangular form, and articulates with the scaphoid bone; the inner, smaller and quadrilateral, articulates with the semi-lunar. The articular surface at the inner side of the bone is called the sigmoid cavity of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna.
Its anterior border, rough and irregular, affords attachment to the anterior ligament of the wrist-joint. Its external border is prolonged obliquely downwards upon the margin of a strong conical projection, the styloid process, which gives attachment by its base to the tendon of the Supinator longus, and by its apex to the external lateral ligament of the wrist-joint. The outer surface of this process is marked by two grooves, which run obliquely downwards and forwards, and are separated from one another by an elevated ridge. The most anterior one gives passage to the tendon of the Extensor ossis metacarpi pollicis, the posterior one to the tendon of the Extensor primi internodii pollicis. Its posterior border is convex, affords attachment to the posterior ligament of the wrist, and is marked by three grooves. The most external is broad, but shallow, and subdivided into two by a slightly elevated ridge. The external groove transmits the tendon of the Extensor carpi radialis longior, the inner one the tendon of the Extensor carpi radialis brevier. Near the centre of the bone is a deep, but narrow, groove, directed obliquely from above downwards and outwards; it transmits
the tendon of the Extensor secundi internodii pollicis. Internally is a broad groove, for the passage of the tendons of the Extensor communis digitorum, and that of the Extensor indicis; the tendon of the Extensor minimi digiti passing through the groove at its point of articulation with the ulna.
Development. By three centres: one for the shaft, and one for each extremity. That for the shaft, makes its appearance near the centre of the bone, soon after the development of the humerus commences. At birth, the shaft is ossified; but the ends of the bone are cartilaginous. About the end of the second year, ossification commences in the lower epiphysis; and about the fifth year, in the upper one. At the age of puberty, the upper epiphysis becomes joined to the shaft; the lower epiphysis becoming united about the twentieth year.
Articulations. With four bones; the humerus, ulna, scaphoid, and semi- Innoi*
Attachment of Muscles. To the tuberosity, the Biceps; to the oblique ridge, the Supinator brevis, Flexor digitorum sublimis, and Flexor longus pollicis; to the shaft (its anterior surface), the Flexor longus pollicis and Pronator quadratus, (its posterior surface) the Extensor ossis metacarpi pollicis, and Extensor primi internodii pollicis; to the outer surface, the Pronator radii teres; and to the styloid process, the Supinator longus.
The Development of Radius
