of Edinburgh, Session 1867 - 68 . 
269 
upper true ribs, and beneath the fibres of the pectoral muscle, which 
is, from the position, direction, and connection of its fibres, I believe 
to be regarded as homologous with the thoracic end of the mam- 
malian rectus. Both subjects were males. In one a longitudinal 
ribbon-shaped muscle arose by a thin expanded tendon, from the 
upper border of the fifth left rib, immediately 7 ’ internal to the at- 
tachment of the serratus magnus. The innermost part of its tendon 
was continuous with the membrane covering the internal intercostal 
muscle, and was attached to the rib at the junction of its osseous and 
cartilaginous portions. From the anterior surface of the fourth rib, 
close to the origin of the serratus magnus, a second and smaller 
origin proceeded. The muscle ascended superficial to the osseous 
parts of the third and second ribs, as high as the first rib, into which 
it was inserted immediately external to the tendon of attachment 
of the subclavius muscle. The muscle was 6 inches long and |ths 
of an inch broad at its widest part. The breadth of the fifth rib 
alone separated it from the upper attachment of the rectus abdo- 
minis. A corresponding muscle existed on the right side. 
In the other subject, a longitudinal muscle — on the right side 
only — arose beneath the pectoralis minor from the upper border of 
the fourth rib two inches to the outer side of the junction of its 
bone and cartilage. It ascended superficial to the third and second 
ribs, to be inserted into the bony part of the first rib, fths of an 
inch external to the attachment of the subclavius. 
In the cat, the otter, the beaver, the porcupine, and various other 
Mammalia, the rectus muscle extends as high as the first rib, into 
which it is inserted, and in this respect the arrangement may be 
compared with that of the occasional human muscles just described. 
In these animals, however, the thoracic and abdominal parts of 
the rectus are directly continuous with each other, whilst in the 
human subject a break, corresponding in the first specimen to the 
fifth rib, and in the second, to the fifth rib and fourth intercostal 
space, occurred ; but this break may be regarded as comparable to 
one of those transverse tendinous intersections, invariably found in 
the abdominal part of the human rectus, and which exist also in 
the recti of the greater number of the Mammalia. These speci- 
mens seem to present as complete a representation of the mam- 
malian arrangement, though in a somewhat different form, as is 
