DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 561 
The supinator longus is double-headed (S./', 8.2’). One belly has a broad fleshy origin 
from the middle and outer side of the humerus at the upper end of the external con- 
dyloid ridge; it ends in a strong tendon, which is inserted broadly upon the outer 
side of the styloid process of the radius. About the middle of the forearm, and at the 
commencement of its tendon, the supinator longus is joined by a strong muscular slip, 
the second head. This additional belly of the supinator arises from the deltoid ridge, 
and, in fact, appears a continuation of the scapular portion of the deltoid, with a mode- 
rately thick belly, but rather smaller than the first head; it goes halfway down the 
radius, ultimately merging with the aforesaid belly at the commencement of the tendon 
of the proper supinator longus. 
The supinator brevis is likewise strong and broad, but almost entirely fleshy (S.2). Its 
broadest, short, aponeurotic origin is from the outer condyle, this origin being crossed 
by the external lateral ligament of the elbow-joint. Another point of origin is from the 
head of the radius; and a third, very small, flat, tendinous slip also comes from the ulna, 
below the coronoid process. The muscular fibres of the supinator brevis cover the side 
and front edge of the radius as far as the prominence at the middle of the bone. 
The eatensor carpi radialis longior (fig. 15, E.c.r.1) arises, in a common fleshy mass, 
along with the extensor carpi radialis brevior (E.c.7.b), from the outer condyloid ridge. 
While their heads of origin therefore form almost a single, elongate, flattened, muscular 
triangle, their tendons are distinctly separate, of equal magnitude, and run side by side to 
the wrist-joint. The tendon of the longior is inserted rather broadly, in an aponeurotic 
manner, into the proximal end of the metacarpal bone of the pollex. The tendon of the 
brevior is inserted in a similar manner into the indicial metacarpal, but rather towards 
the radial side of its dorsal surface—the two, however, together forming a broad aponeu- 
rotic bridge between the roots of the first and second metacarpal bones; the latter is 
overlain by the great pollicial tendon of the muscle. 
Extensor pollicis et indicis—The very powerful muscle which I shall describe under 
the above denomination, may, in fact, represent the extensor primi internodii pollicis, 
and not be, as I have named it, the extensor pollicis et indicis. The name proprius 
pollicis is appropriate functionally ; for through the enormous tendon is extension and 
power in the pollex chiefly derived. By whatever name the muscle is noticed, it is 
distinguished by its possessing an unusually broad, pyramidal, fleshy belly, which arises 
from the hinder end and outer projecting grooved side of the olecranon process, and 
from the upper and posterior half of the ulna. Its extraordinarily broad and powerful 
tendon commences just about the distal end of the ulna, and, crossing the dorsum of 
the manus, is inserted into the proximal end of the proximal phalanx of the pollex. 
At this part it widens out and intermingles with the sheath of fibrous tissue here form- 
ing the periosteal covering of the bone. 
Extensor ossis metacarpi pollicis.—This muscle is broad, flat, fleshy, and strong. The 
origin is from the outer surface of the olecranon, and from the ulna to as far as about 
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