101 
Royal Society of Edinburgh. 
by recent observations on the inner obscure ring of Saturn. The 
limb of the planet is seen through the substance of this ring, not 
refracted, as it would be through a gas or fluid, but in its true posi- 
tion, as would be the case if the light passed through interstices 
between the separate particles composing the ring. 
As the whole investigations are shortly to be published in a sepa- 
rate form, the mathematical methods employed were not laid before 
the Society. 
3. On a peculiar Ligament connecting the opposite Ribs in 
certain Yertebrata. By Dr Cleland. Communicated by 
Professor Goodsir. 
While examining the bones of a seal which had been for some 
time in maceration, the author observed that, in detaching one of 
the ribs from the vertebral column, a long ligament, connected to 
the head of the former, emerged from the intercostal foramen. 
It was then found that the right and left rib in all the pairs articu- 
lating with two vertebrae were connected across the mesial plane by 
a ligament which was attached at each end to a depression on the 
lower part of the continuous convex cartilaginous surface of the head 
of the rib, and was lodged in a tube on the floor of the spinal canal, 
formed by a groove on the upper surface of the corresponding inter- 
vertebral disc covered by the superior longitudinal ligament, and 
lined by a synovial membrane common to the tube, the ligament 
contained in it, and the entire heads of both the ribs. 
It appeared probable that this peculiar transverse intercostal liga- 
ment would be found developed in the mammalia directly as the flexi- 
bility of the spine. 
In the weasel and squirrel it is fully developed ; also in the lion, 
fox, and dog ; but in the three latter the single synovial membrane 
common to the entire arrangement only lines the groove on the su- 
perior edge of the intervertebral disc and the under surface of the 
ligament, the latter being thus in contact above with the superior 
longitudinal ligament of the spine. 
In the sheep and horse the fibres of the anterior half of the liga- 
ment are attached midway to the posterior superior margin of the 
body of the vertebrae in front. In the sheep there are two synovial 
membranes for the head of each rib,— -the posterior on each side com- 
