062 DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 
the middle of the latter. As usual, its direction is slanting, or crossing that of the 
forearm, and it winds round the styloid process of the radius. Its tendon lies in a radial 
malleolar groove and passes underneath the binding ligament, being at length inserted 
by a remarkably powerful broad tendon into the proximal and anterior or outer corner 
of the metacarpal bone of the pollex. 
The extensor primi and extensor secundi internodii pollicis are wanting. 
Common Extensors.—There appears to be a double set of long deep extensor muscles 
of the forearm in the pectoral extremity of the Sea-lion. If these represent different 
muscles, they nevertheless arise by fleshy fibres in one common mass from the outer 
condyle, and proceed together downwards in a united condition for three-quarters the 
length of the forearm. 
1. The anterior portion of the above muscular belly may more truly be regarded as 
representing the extensor communis digitorum. Its origin is as above stated. From 
below the middle of the forearm downwards it is superficially covered with tendinous 
aponeurotic fibres. Opposite the lower end of the radius it divides into three broadish 
tendons, which supply respectively the index, middle and fourth digits (see .c.d). 
The first two, or inner tendons, separate below the wrist-joint; the third, or outer one, 
divaricates higher up than these two. At the proximal ends of the first phalanges 
each tendon spreads out, so that at the distal end of the phalanx it covers, as by an 
aponeurosis, the whole breadth of the bone, and is finally inserted into the proximal 
end of the second phalanx. It may furthermore be remarked that its fibres interblend 
with others on either side of the digit, which go on as far as the proximal end of the 
last digit. 
2. The middle portion of the common muscular origin, while intimately united above, 
becomes by degrees definite and distinct as it proceeds downwards. Dissection shows 
such an intervention of cellular tissue between the muscular fibres as to constitute a 
muscular belly, extensor medii digiti (Z.me.d). This muscular belly is much smaller 
and less broad than the first portion, already described. It divides at the level of the 
divarication of the outermost tendon of the former part into two tendons, the largest 
of which is inserted into the fifth digit, and ends in a similar manner as the three 
already spoken of in describing the first portion of the muscle. The smaller inner 
tendon lies deeper than the outer one, and proceeds below the fourth digital tendon to 
the outer side of the third digit, mingling at last with the common fibrous tendinous 
expansion of the digit. 
3. The third or outermost portion of the common extensor muscle may be said to 
represent the extensor minimi digiti (Z.m.d). This appears as a narrow muscular belly 
lying alongside the middle extensor belly already spoken of. It likewise ends, as the 
middle portion does, in two tendons, but differs in these tendons being more nearly 
equal in size. The outermost tendon is inserted into the distal end of the outside of 
the fifth metatarsal bone. The innermost tendon proceeds as far as the divergence of 
