DR. J. MURIE ON THE ANATOMY OF THE SEHA-LION. 555 
region, where the anterior border is in a line with the shoulder-joint, and the posterior 
border covers the axilla proper. This humero-axillary end terminates by a somewhat 
semilunar-shaped fascia, the anterior part of which is firmly inserted into the humerus 
from the head of the bone to below its middle; the posterior or axillary part joins the 
fascia of the forearm on the inner side. 
The second division is the largest and most elongated (P.ma*). It arises upon 
the thorax opposite the first and second ribs, and reaches backwards in the median 
sternal line to the ensiform cartilage. The intersecting fibres are directed forwards 
and outwards, and proceed to the axilla, where they end abruptly in a semilunar form, 
much in the same manner as does the superior layer already described. Their insertion 
is also partly by a fascia which joins the aponeurotic fascia of the forearm; but this 
layer is attached by delicate fibres more over the humerus and upon the biceps muscle 
than is the superficial layer. A strong aponeurotic tendon, however, goes to be inserted 
along with the portion of the first division already spoken of. 
The third and smallest division is a narrow strip, quite separate from the others, 
which arises from the manubrium and passes in a straight line outwards towards the 
head of the humerus, near which its fibres join those of the superficial layer (or first 
portion), but rather below it. Though including the above third muscle among the 
peciorales, I have no hesitation in classing it as the sterno-scapular (St.s). 
Remarks concerning the Pectorals.—With such a modified pectoral extremity as is 
possessed by the Sea-lion, and one so well fitted in many respects for sweeping forcibly 
through a watery element, it would be strange if we did not meet with some muscular 
coadaptations in the member. While the digits are in a- great measure held in 
abeyance as grasping or burrowing implements, the whole palm (and, indeed, forearm) 
is called into active unison during the propulsive strokes of swimming. As we have 
seen, the upper arm is lashed forwards chiefly by the great cephalo-humeral, partially 
rotated by the deltoid, and powerfully dragged backwards by the relatively enormous 
latissimus dorsi, great pectoral, and extensive panniculus carnosus. But combination 
of force applied ever so much to the humeral end of the limb would not of itself effect 
the power and steadiness of the sweep which the forearm and flipper are capable of, 
unless the latter were duly strengthened and rendered somewhat rigid. ‘This to some 
extent is provided for in the dense skin and firm superficial aponeurotic sheath which 
encase the muscular apparatus. More, however, seems to be required to transmit the 
power from the proximal to the distal end of the limb, and, it may be, to regulate the 
tension of the parts. Whatever is the precise mechanical explanation, or the necessity 
for extra superficial muscular development, we have at least a well-marked example of it 
in the inner radio-ulnar region of the animal under consideration. It has been shown 
that the axillary portions of the panniculus carnosus and latissimus dorsi stretch across 
the inner aspect of the cubital region from the one border almost to the other; and in 
so doing they limit to some extent the muscular arc, whereof the base is the body 
