166 COUES ON THE OSTEOLOGY 



The triceps extensor of the forearm is divided into two perfectly distinct muscles, which 

 may be called the " long " and " short." The former arises fleshy from the scapula half an 

 inch below the glenoid fossa, passes as a stout, fusiform, fleshy belly to within an inch and a 

 half of the olecranon, where it becomes tendinous; runs through a groove in the outer con- 

 dyle of the humerus, to be inserted into the olecranon on its radial aspect. About an inch 

 from its origin it gives off a small but distinct flat tendinous slip, which passes obliquely 

 upwards and backwards to be inserted into the humerus ; it being joined by a similar slip 

 given off by the latissimus dorsi, which is inserted with it. 



The other portion of the extensor is perfectly distinct, having a different origin and 

 separate tendon of insertion. It arises from the posterior aspect of the shaft of the hume- 

 rus for nearly its whole length ; becomes tendinous near the elbow, and passing through a 

 separate groove in the inner condyle, is inserted into the corresponding side of the olecra- 

 non, just opposite the insertion of the longer extensor. 



Pronator radii teres ; Supinator brcvis. Arising respectively from the internal and external 

 condyle, these two muscles converge towards their insertions into the radius exactly 

 opposite each other. They directly antagonize each other ; but, from the almost complete 

 absence of pronation and supination in a bird's antibrachium, probably act together, 

 and thus serve to steady the radius. 



Extensor metacarpi radialis longior. As usual, a large muscle, the first one given off on 

 the radial aspect of the limb. Arises high up on the external condyle by a flattened tendon, 

 which soon changes to a fusiform fleshy belly ; again changes, about the middle of the 

 forearm, to a rounded tendon ; this passes along a deep groove in the head of the radius, 

 to be inserted into the radial aspect of the metacarpus. In its passage along the radial 

 groove it is accompanied by the tendon of the next muscle. 



" Extensor metacarpi radialis brevior." (Extensor proprius pollicis ?) This very slender 

 small muscle arises from, and lies along, the ulnar aspect of the radius, its delicate tendon 

 passing forwards along the radial groove with that of the preceding, to be inserted into 

 the base of the pollex. Its tendon is more or less blended with that of the preceding ; 

 and any motion which it can impress upon the pollex must at best be but slight. It ap- 

 pears to have rather the effect of an auxiliary extensor of the metacarpus, aiding the action 

 of the preceding. 



A small, very slender, but long muscle arises from the internal condyle ; lies along the 

 ulnar aspect of the radius, beneath the preceding ; its delicate rounded tendon passes 

 through a notch in the head of the ulna, and runs obliquely along the side of the meta- 

 carpus ; divides into two slips, one of which goes to the base of the pollex, the other to 

 the base of the first digit. This muscle adducts the thumb, and bends the metacarpus 

 upon the anti-brachium. 



Flexor metacarpi radialis. Arises from nearly the whole length of the radial aspect of the 

 ulna, and from the inferior aspect of that bone for its distal fourth. Its tendon passes ob- 

 liquely over to the head of the radius ; and is received into a deep groove, which carries it 

 transversely across to the outer aspect of the wrist joint, where it dips deeply down to its 

 insertion into the head of the metacarpus. This muscle seems to act as a flexor in the 

 following interesting manner: When the hand is extended, or rather abducted, the head 

 of the metacarpal bone, revolving in the radio-carpal articulation, carries with it the tendon, 

 by which means the muscle is put upon the stretch. The contraction of the muscle, there- 

 fore, will of course tend to restore the bone to its original position, and thus fold or adduct 

 the pinion. 



