" If we observe the bones of the anterior extremity in the horse, we shall see that the scapula is oblique to the chest, the humerus oblique to the scapula, and the bones of the fore-arm at an angle with the humerus. Were these bones connected together in a straight line, end to end, the shock of alighting would be conveyed through a solid column, and the bones of the foot or the joints would suffer from the concussion. When the rider is thrown forwards on his hands, and more certainly when he is pitched on his shoulder, the collar-bone is broken, because in man this bone forms a link of connexion between the shoulder and the trunk, so as to receive the whole shock ; and the same would happen in the horse, the stag, and all quadrupeds of great strength and swiftness, were not the scapula sustained by muscles and not by bone, and did not the bones recoil and fold up." " The horse jockeyruns his hand down the horse's neck in a knowing way and says, this horse has got a heavy shoulder, he is a slow horse.' He is right, but he does not under stand the matter ; it is not possible that the shoulder can be too much loaded with muscle, for muscle is the source of motion and bestows power. What the jockey feels and forms his judgement on is the abrupt transition from the neck to the shoulder, which, in a horse for the turf, ought to be a smooth undulating surface. This abruptness or prominence of the shoulder is a consequence of the upright position of the scapula ; the sloping and light shoulder results from its obliquity. An upright shoulder is the mark of a stumbling horse—it does not revolve easily to throw forward the foot."* A comparison between the skeleton of the anterior extremity in the elephant and in one of the stag kind illustrates how the oblique position of the scapula is favourable to rapidity of motion, while the upright position is that most calculated for supporting weight. In the elephant the glenoid cavity of the scapula is placed vertically over the head of the humerus, and all the other component parts of the limb are similarly disposed, so as to form a complete pillar of support for the trunk. hence the attitude of standing in the elephant requires but slight muscular effort, and in this position lie is in such complete repose as often to obtain sleep. In this animal, then, the angle between the scapula and humerus is nearly obliterated, but in the stag it approaches closely to a right angle, the scapula is oblique to the ribs, and the humerus to the scapula. The rule seems to be that where the pectoral extremity is chiefly a pillar of, support, the aspect of the glenoid cavity is nearly vertically downwards. If free dom and rapidity of motion be required in addition to strength as a member of support, the trunk being lighter, the scapula is oblique, and consequently the glenoid cavity looks downwards and forwards ; or if the limb be not used to support the trunk, then the aspect of the glenoid cavity is no longer downwards but outwards, as in man.
Structurc.—The greatest part of the scapula is composed of very thin almost papymceous compact substance; but its processes, and the enlargements at its edges and angles, contain reticular tissue.
Dcvelopement.—This bone is developed by six points of ossification; one for the body, and five supplementary ones, viz. one for the corticoid process, two for the acromion, one for the posterior border of the bone, arid one for its inferior angle. The ossification of the body commences about the second month, and the spine appears in the third month as a growth from the posterior surface of the scapula.
The union of the several epiphyses is not completed till late, and it is not until after the fifteenth year that the ossification is finished.
The bones of the upper extremity, properly so called, are the humerus, radius, ulna, and bones of the hand.
Humerus, (os braehii ; Fr. ros du bras; Germ. des Obcrarmbein). This is the longest bone of the upper extremity; it is situated between the scapula and forearm, being, as it were, suspended by muscle and ligament from the former.
Like all long bones, the humerus consists of a shaft and two extremities. The superior extremity is formed by a smooth and rounded convexity, rather less than half a sphere ; a slight depression in, or constriction of, the bone, most manifest above, marks the limit of this articular eminence. The eminence is called the head of the humerus; the constric tion indicates what is denominated the anato mical neck if the bone, being that portion which connects the head to the shaft, and analogous to the more developed neck of the thigh-boric. The axis of the neck is but a continuation of that of the head, and passes in a direction from within outwards and down wards, forming an obtuse angle with the axis of the shaft. The head of the humerus is entirely covered by articular cartilage, and arti culates with the glenoid cavity of the scapula, to which, however, it obviously does not at all correspond in dimensions.
The inferior part of the anatomical neck of the humerus is very slightly marked, and is continued in a smooth declivity slightly con cave from above downwards, into the shaft of the bone. Its superior part is more distinct, and the depth of the groove here seems in a great degree owing to the prominence of two bony protuberances, one situated anteriorly, called the lesser tuberosity, arid the other pos teriorly, denominated the greater tuberosity.
The lesser tuberosity of the humerus ( tuber culum minus) is somewhat conical in shape, and inferiorly it ends in a smooth, rounded bony ridge (spine tuberculi minaris), which extends downwards and inwards, gradually diminishing in prominence till it is lost in the shaft of the bone at the inner part of its ante rior surface. The lesser tuberosity gives in sertion to the tendon of the subscapularis muscle, and the ridge or spine last described forms the anterior and internal boundary of the bicipital groove.
The greater tuberosity (tuberculum majus, externum s. posterius) forms a considerable prominence on the upper and outer part of the humerus, being the most external part in that situation and easily to be felt under the integuments. Superiorly the constriction cor responding to the anatomical neck separates it from the head of the humerus; inferiorly it is continued into and gradually lost in the shaft of the bone at its outer part. A very distinct and prominent ridge Opera tubereuli ntajoris) is continued from its anterior extremity down wards and inclining very slightly inwards, which terminates about the middle of the an terior surface of the bone, just internal to the deltoid ridge. This ridge is most prominent but smooth in its upper third, in its inferior two-thirds it is less prominent but rough; it forms the posterior boundary of the bicipital groove. On the greater tuberosity three dis tioet surfaces are marked, to the anterior of which the supra-spinatus muscle is attached, to the middle the infra-spinatus, and to the posterior the teres minor.