Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/877

Rh A&amp;lt;5 UPPER LIMB.] 8U}jra- or praj-spwicws fossa, and one below the spine, the infra- or post-spinous fossa. The spine arches forwards, to end in a broad flattened process, the acromion, which has an oval articular surface for the clavicle ; both spine and acromion are largely developed in the human Bcapula in correlation with the great size of the trapczius and deltoid muscles, which are con cerned in the elevation and ab duction of the upper limb. The borders of the scapula, directed upwards, backwards, and down wards, give attachment to several muscles. The angles are inferior, supero-posterior, and supero-an- terior. The supero-anterior is the most important ; it is truncated, and presents a large, shallow, oval, smooth surface, the glenoid fossa, for articulation with the humerus, to form the shoulder joint. Over hanging the glenoid fossa is a curved beak-like process, the coracoid, which is of importance as corresponding with the separate coracoid bone of birds and reptiles. The line of demarcation between it and the scapula proper is marked on the upper border of the scapula by the supra-scapular notch. The Humerus, or bone of the Upper Arm (Fig. 9), is a long bone, and consists of a shaft and two extremities. The upper extremity _ i.1 1 FlG of this bone possesses a convex spheroidal smooth surface, the head, for articulation with the glenoid fossa of the scapula it is surrounded by a narrow con stricted neck, and where the neck and shaft become continuous with each other, two processes or tuberosities are to which are attached the rotator muscles arising from the scapular fossce. Between the tuberosities is a groove in which the long tendon of the biceps rests. A line drawn through, the head of the humerus perpendicular to the middle of its articular surface, forms with the axis of the shaft of the bone an angle of 40. The shaft of the humerus is cylindriform above, but flattened and expanded below ; about midway down the outer surface is a rough ridge for the insertion of the deltoid muscle, and on the inner surface another rough mark for the insertion of the coraco-brachialis. The demarcation between the cylindri form and expanded parts of the shaft is marked by a shallow groove winding round the back of the bone, in which the musculo-spiral nerve is lodged. The lower extremity of the humerus consists of an articular and a non-articular portion. The articular presents a small head or capitellum for the radius, and a pulley or trochlea for the movements of the ulna in flexion and extension of the limb. The non- articular part consists of two condyloid eminences, internal and external. From the external, or epi- condyle, a ridge passes for some distance along the outer border of the bone ; it gives origin to the supinator and extensor muscles in the fore-arm. From the internal emi nence, or epi-trochlca, a ridge passes up the inner border of the shaft of the bone; this eminence gives origin to the The Appendicalar Skele ton of the Left Upper Limb. CL, clavicle ; Sc, scapula ; Ac, acromion process ; Cr, coracoid process of scapula; II, humerus; H, radius ; U, ulna ; C, opposite the eight carpal bones ; 3Ic, op posite the five metacarpal bones ; P, polios, or thumb ; II. index, III. middle, IV. ring, V. little finger. found. 827 pronator and flexor muscles in the fore-arm. In nearly two per cent of the bodies examined in the anatomy-rooms in the university of Edinburgh, a hooked process has been seen projecting from the shaft of the bone, about 2 inches above the epi-trochlea ; this process is connected to the epi-trochlea by a fibrous band, so as to form a foramen, which has been called mpra-condyloid. In these cases the median nerve invariably passes through the foramen, and not unfrequently is accompanied by the brachial artery. In the feline carnivora and some other mammals a foramen constantly occurs in this part of the hunierus, through which, as a rule, both nerve and artery proceed, though in the common seal it transmits only the nerve. Before describing the two bones of the fore-arm, the anatomist should note the range of movement which can take place between them. In one position, which is called supine, they lie parallel to each other, the radius being the more external bone, and the palm of the hand being directed forwards ; in the other or prone position the radius crosses obliquely in front of the ulna, and the palm of the hand is directed backwards. Not only the bones of the fore-arm, but those of the hand are supposed to be ia the supine position when they are described. The Radius (Fig. 9) is the outer bone of the Fore-arm, and Radius, like all long bones possesses a shaft and two extremities. The upper extremity or head has a shallow, smooth cup for moving on the capitellum of the humerus ; the outer margin of the cup is also smooth, for articulation with the ulna and annular ligament; below the cup is a constricted neck, and immediately below the neck a tuberosity for the insertion of the biceps. The shaft of the bone possesses three surfaces for the attachment of muscles, and a sharp inner border for the interosseous membrane. The lower end of the bone is much broader than the upper, and is marked posteriorly by grooves for the lodgment of tendons passing to the back of the hand : from its outer border a pointed styloid process projects downwards; its inner border has a smooth shallow fossa for articulation with the ulna, and its broad lower surface is smooth and concave, for articula tion with the scaphoid and semilunar bones of the wrist. The Ulna (Fig. 9) is also a long bone. Its upper end is Ulna, subdivided into two strong processes by a deep fossa, the greater sigmoid cavity, which possesses a smooth surface for articulation with the trochlea of the humerus. The anterior or coronoid process is marked by an oblique ridge for the insertion of the brachialis anticus, whilst the pos terior or olccranon process gives insertion to the large triceps muscle of the upper arm. Immediately below the outer border of the great sigrnoid cavity is the small sigmoid cavity for articulation with the side of the head of the radius. The shaft of the bone possesses three surfaces for the attachment of muscles, and a sharp outer border for the interosseous membrane. The lower end, much smaller than the upper, has a pointed styloid process and a smooth articular surface, the outer portion of which is for the lower end of the radius, the lower part for moving on a cartilage of the wrist joint called the triangular fibro- cartilage. The Hand consists of the Carpus or wrist, of the Meta- Hand, carpus or palm, and of the free Digits, the thumb and four fingers. Anatomists describe it with the palm turned to. the front, and with its axis in line with the axis of the fore-arm. The Carpal or &quot;Wrist bones (Fig. 9) are eight in number Carpus, and small in size : they are arranged in two rows, a proximal, i.e. a row next the fore- arm, consisting of the scaphoid, semilunar, cuneiform, and pisiform ; and a distal, i.e. a row next the bones of the palm, consisting of a trapezium, trapezoid, os magnum, and unciform ; the bones in each row being named in the order they are met with,