158 THE SKELETON. 



applied in these cases should be rather wider than the limb, so as to prevent any lateral pressure 

 on the bones. For in these cases there is a greater liability to gangrene from the pressure of the 

 splints than in other parts of the body. This is no doubt due principally to two causes: (1) 

 the flexion of the forearm compressing to a certain extent the brachial artery and retarding the 

 flow of blood to the limb ; and (2) the superficial position of the two main arteries of the forearm 

 in a part of their course, and their liability to be compressed by the splints. The special 

 fractures of the ulna are (1) Fracture of the olecranon. This may be caused by direct violence, 

 falls on the elbow with the forearm flexed, or by muscular action by tlv^aidden contraction of 

 the triceps. The most common place for the fracture to occur is at tne constricted portion 

 where the olecranon joins the shaft of the bone, and the fracture may be either transverse or 

 oblique ; but any part may be broken, even a thin shell may be torn off. Fractures from direct 

 violence are occasionally comminuted. The displacement is sometimes very-slight, owing to the 

 fibrous structures around the process not being torn. (2) Fracture of the coronoid process some- 

 times occurs as a complication of dislocation backward of the bones of the forearm, but it is 

 doubtful if it ever occurs as an uncomplicated injury. (3) Fractures of the shaft of the ulna 

 may occur at any part, but usually take place at the middle of the bone or a little below it. 

 They are almost always the result of direct violence. (4) The styloid process may be knocked 

 off by direct violence. Fractures of the radius consist of ( 1 ) Fracture of the head of the bone ; 

 this generally occurs in conjunction with some other lesion, but may occur as an uncomplicated 

 injury. (2) Fracture of the neck may also take place, but is generally complicated with other 

 injury. (3) Fractures of the shaft of the radius are very common, and may take place at any 

 part of the bone. They may take place from either direct or indirect violence. In fractures of the 

 upper third of the shaft of the bone, that is to say, above the insertion of the Pronator radii teres, 

 the displacement is very great. The upper fragment is strongly supinated by the Biceps and Supi- 

 nator brevis, and flexed by the Biceps ; while the lower fragment is pronated and drawn toward 

 the ulna by the two pronators. If such a fracture is put up in the ordinary position, midway 

 between supination and pronation, the fracture will unite with the upper fragment in a position 

 of supination, and the lower one in the mid-position, and thus considerable impairment of the 

 movements of the hand will result. The limb should be put up with the forearm supinated. (4) 

 The most important fracture of the radius is that of the lower end (Colles's fracture). The fract- 

 ure is transverse, and generally takes place about an inch from the lower extremity. It is caused 

 by falls on the palm of the hand, and is an injury of advanced life, occurring more frequently in 

 the female than the male. In consequence of the manner in which the fracture is caused, the 

 upper fragment becomes driven into the lower, and impact ion is the result : or else the lower frag- 

 ment becomes split up into two or more pieces, so that no fixation occurs. Separation of the lower 

 epiphysis of the radius may take place in the young. This injury and Colles's fracture may be 

 distinguished from other injuries in this neighborhood especially dislocation, with which it is 

 liable to be confounded by observing the relative positions of the styloid processes of the ulna 

 and radius. In the natural condition of parts, with the arm hanging by the side, the styloid pro- 

 cess of the radius is on a lower level than that of the ulna; that is to say, nearer the ground. 

 After fracture or separation of the epiphysis this process is on the same or higher level than that 

 of the ulna, whereas it would be unaltered in position in dislocation. 



THE HAND. 



The skeleton of the Hand is subdivided into three segments the Carpus or 

 wrist-bones ; the Metacarpus or bones of the palm ; and the Phalanges or bones 

 of the digits. 



The Carpus. 



The bones of the Carpus (xao~6z, the wrist), eight in number, are arranged in 

 two rows. Those of the upper row, enumerated from the radial to the ulnar 

 side, are the scaphoid, semihmar, cuneiform, and pisiform ; those of the lower 

 row, enumerated in the same order, are the trapezium, trapezoid, os magnum, and 

 unciform. 



Common Characters of the Carpal Bones. 



Each bone (excepting the pisiform) presents six surfaces. Of these the anterior 

 or palmar and the posterior or dorsal are rough for ligamentous attachment, 

 the dorsal surface being the broader, except in the scaphoid and semilunar. The 

 superior or proximal and inferior or distal are articular, the superior generally 

 convex, the inferior concave ; and the internal and external are also articular when 

 in contact with contiguous bones, otherwise rough and tubercular. The structure 

 in all is similar, consisting of cancellous tissue enclosed in a layer of compact bone. 

 Each bone is also developed from a single centre of ossification. 



