Near the apex of the cone formed by the chest the upper or- thoracic limbs are attached. They are composed of four parts,—the shoulder, arm, fore-arm, and hand. The two bones of the shoulder are the scapula, which is attached by muscles to the upper part of the back, and the clavicle or collar-bone, which extends from the sternum to the scapula, embracing the top of the chest At the angle formed by the superior border and the external edge of the scapula an articular surface, called the glenoid cavity, receives the upper extremity or head of the humerus, the bone of the arm, which articulates at the elbow with the ulna and the radius, the two bones of the fore-arm; these form with the carpus the wrist-joint, which unites the forearm to the hand. The deltoid, the great dorsal and great pectoral, and other less powerful muscles, combine to form the shoulder, and give motion to the humerus. The triceps and biceps of the arm, etc, which surround the humerus, flex or extend the fore-arm and turn it on its axis; and numerous muscles cover the fore-arm and move the hand.
The articulation of the humerus with the scapula or the shoulder-joint is, of all joints, the one that permits the most extended movement. The shallowness of the glenoid cavity permits great freedom of motion to the rounded head of the humerus. Thus the arm, which hangs parallel with the body in a state of repose, can be raised vertically to the head, laterally forward so as almost to enfold the chest, and also backward, though in a more limited degree; it can be turned on its axis in all these positions, and in the movement of circumduction it describes a very flat cone, the base of which, especially in front, approaches the apex.
The elbow-joint is one of the most complicated in the whole system. The lower extremity of the humerus, and the upper extremities of the ulna and the radius, are adapted to, and interlock with each other by a series of rounded surfaces and pulley-grooves, which permit the fore-arm to flex itself forwards upon the arm; while a protuberance of the ulna, the olecranon, which forms the projecting part of the elbow, limits the backward movement by resting in a cavity of the humerus. It is into the olecranon that the tendon of the triceps of the arm, the principal extensor of the fore-arm, is inserted, and we shall see the analogy farther on between this process and the knee-pan.
The movements of the fore-arm singularly multiply by their application those of the arm. The radius and ulna may be placed in contact with the humerus by flexion, and again the radius turns on its own axis, without either the ulna or the humerus taking part in this movement, which is called pronation or supination, according as the palm of the hand is turned outward or inward.
But what renders the thoracic limb a perfect organ, that which explains the variety and extent of its movements, and which gives them all their value, is the hand; that admirable instrument which in its perfection belongs only to the human race.
The hand is elegant and beautiful in form. Its isolation, its contour—denned without stiffness—the delicacy of its mould, the mobility of its different parts, and the variety in their tints, make of it a being by itself in the human body, and give it an expression and a physiognomy. Completely developed even in infancy, it presents a most attractive model and an inexhaustible subject of study to the artist Its structure has led many philosophers to think that it is to it alone that man owes his superiority to the animals, and to attribute to it the greatest influence over the intellectual faculties. But the study of man shows that we must reverse this proposition. The hand is only the instrument of the intellect, the perfection of the one is necessarily dependent upon that of the other, and the hand of man, like every other part of his being, has no equal in the animal kingdom.
As for seeing in the greater or less perfection of the hand a sign of the degree of intelligence, and carrying it so far as to distinguish between the hand of a man of talent and genius, and that of a fool or a man of moderate ability—this is a theory which, speciously presented, might perhaps be entertained as a subject having curious aspects, but on no other ground. In short, if the hand of the idiot is alike badly developed with the brain—if we believe that an arrested development of the lingers, or the presence of supernumerary ones, are signs of degeneration in the race—are we to conclude that perfection of the thoracic limbs is the rule, as has been said, in men of eminence? We need not go so far back as Esop for an example of a great mind in a deformed body. Conde, Luxembourg, Pope, and other illustrious and celebrated men, were victims of rickets. They had long and knotty hands, one of the most constant signs of this malady. If men of inferior intelligence often have thick and inflexible hands, it is because they are often bora under conditions which impose rough work upon them. They receive as a heritage, with the toil of their fathers, this clumsiness of form, which is the consequence of this toil. The hand of the man who is not forced by his position to manual labour is always finer and more delicate than that of the workman, and he transmits to his children this detail of conformation as well as the general resemblance. The delicacy of the limbs, the principal element of their elegance, is therefore a sign of race rather than of intelligence, and belongs especially to the oriental; The hand of a European cannot enter the guard of an Indian sword or poniard. Shall we conclude from that that the Anglo-Saxon or the Norman has less intelligence than the Arab or the Hindoo? De Blainville relates that Recamier attached a certain importance to the form of the hand, and was accustomed to examine those of his pupils with this idea. "Mine," he adds, "were, like the others, submitted to the inspection of the master, and the result was not unfavourable to me." Recamier being present, confirmed the statement of the former pupil of the Hotel-Dieu, now become an eminent naturalist But the hand of De Blainville was neither fine nor elegant; it was a well-made, vigorous, and muscular hand, like the body to which it belonged; equally skilful, in fact, in holding a sword, a pencil, or a scalpel.