66 
Proceedings of the Royal Society 
double, making together twenty-seven specimens of the muscle. 
The variations which it exhibited in its attachments, size, and 
shape, were then described. In no case were its fibres continuous 
with those of the rectus abdominis, or were tendinous intersections 
found in it, but it mostly arose either from the flattened tendon of 
the external oblique muscle of the abdomen, or from the cartilages 
of the lower true ribs, and in many instances it was continuous at 
its upper end with the sternal tendon of one or both sterno-mastoids, 
whilst in others it was inserted into the aponeurosis covering the 
pectoralis major. It was always superficial to the great pectoral 
muscle. Of the single specimens, four occurred on the right side, 
two on the left ; whilst in the remaining five it arose on one side of 
the middle line, and was inserted either altogether or in part on 
the opposite side. It formed an excellent illustration of the truth 
of the general statement, that occasional and rudimentary struc- 
tures are especially liable to variations in arrangement. 
A sketch of the history of the muscle, from the first obser- 
vation by Cabrolius in 1604, was then given, and the various 
opinions as to its morphology were discussed. In opposition to the 
view usually entertained by anatomists, the author contended that 
it was not an upward extension of the rectus abdominis, such as is 
so frequently seen in the mammalia, so that the name rectus ster- 
nalis, or stern alis brutorum, usually applied to it, is not appropriate. 
For it was not continuous with the rectus, and was placed super- 
ficial to the pectoralis, whilst the anterior end of the mammalian 
rectus is always continuous with its abdominal part, and, moreover, 
concealed by the pectoral muscle ; and further, another muscle 
has occasionally been seen in man which, differing in its position 
from the sternalis, lying under cover of the great pectoral muscle 
next the ribs, is undoubtedly to be regarded as homologous with 
the anterior end of the mammalian rectus. 
The sternalis muscle, from many of its relations, seems to be most 
closely allied to the panniculus carnosus, or great skin muscle of 
the quadruped, and may perhaps be regarded as an additional rudi- 
ment of that muscle, occasionally present in man, though it must 
be admitted that the human platysma (which is generally acknow- 
ledged to represent the panniculus) lies on a plane superficial to the 
fibres of the sternalis in those individuals in whom they coexist. 
