DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 551 
muscle, as it diverges from the previous one, proceeds to be inserted into the third rib 
and the interspace before it, just where the rib becomes cartilaginous. Both the 
scalenus anticus and posticus are of moderate size. 
Supracostal.—tn the species of Otaria under consideration, as well as in the Common 
and Ringed Seals (Phoca vitulina and P. fwtida), 1 have found a broad, flat, but strong 
layer of muscle representing the above (Sct, figs. 21 & 33). In the Sea-lion it lies to 
the sternal side of the scalenus anticus, a small portion of its origin being covered by 
that muscle. This well-marked supracostal arises from the middle third of the first 
rib, broad, and partly tendinous. The fibres are directed in a slanting manner towards 
the sternum, downwards and backwards, and are inserted into the cartilage of the third 
rib and upon the costal interspace behind. 
Intercostal Muscles.—Vhese (It) are remarkably broad and fleshy planes of fibres, 
and almost devoid of the tendinous intersections commonly found in them. The layer 
termed the intercostales externi reaches from the head of the rib to about the middle 
of the sternal cartilages. The sternal ends, which slant very much, are inserted in such 
a manner that the portion which is attached to the rib itself is prolonged beyond the 
other. 
Triangularis sterni (fig. 25, T.s).—In accordance with the length of the thorax, this 
muscle is long; and relatively to its transverse diameter it is broad. It is composed of 
five pyramidal or triangular-shaped flat and strong slips. The base and origin of each 
of these is the sternum, upon its pleural surface, but not quite reaching the median line. 
Their fibres are directed upwards and outwards; and the five slips are inserted into the 
seventh, sixth, fifth, fourth, and third rib-cartilages respectively. Towards the sternal 
ends the inner surface is glistening and tendinous, but at the rib-cartilages strongly 
muscular. ach slip crosses one portion of rib-cartilage behind it before reaching its 
own insertion. 
Diaphragm.—This extensive plane of inspiratory muscular and tendinous fibres, as 
might be expected, is well developed. Its substance is not so thick as obtains in some 
Carnivorous animals, ¢. g. the Lion; but the fleshy fibres are equally and evenly dis- 
tributed throughout the whole of the organ. It is further overlain and entirely covered 
both on its thoracic and abdominal surfaces by a thick layer of strong white glistening 
aponeurotic fibres, which nevertheless permits of the fleshy fibres beneath being traced. 
The distribution of the thicker tendinous portions of the diaphragm (the so-called 
central or cordiform tendo diaphragmatis), the direction of the ensheathed muscular 
fibres, and the openings are best observed upon the thoracic surface; I shall conse- 
quently describe them from that point of view. Figure 19, Pl. LXX., shows in a 
partially diagrammatic manner the diaphragm as seen from the thorax. 
The central tendon of human anatomy (c) is represented by a fibrous interspace, free 
from muscle, of a spearheaded shape, and about a couple of inches long by fully an 
inch broad, The two fibrous alar tendons (r and 7) are given off from the neck of this 
VOL. VII.—PART Vill. January, 1872. 4x 
