1909.] | ON ELASTIC MECHANISMS IN FISHES AND A SNAKE. 201 
March 2, 1909. 
G. A. BouLencer, Esq., F.R.S., Vice-President, 
in the Chair. 
Mr. R. H. Burne, F.Z.S., exhibited and remarked on the followin g 
specimens of certain elastic mechanisms in Fishes and Reptiles :— 
“J. The ligamentum longitudinale ventrale of a Shad (Clupea 
alosa). 
The ligament lies in the cavity of the aorta suspended by a 
longitudinal fold of its dorsal wall. In front it is firmly attached 
to the basioccipital ; in the trunk region it is free except for the 
mesentery-like fold of the aortic wall by which it is suspended 
(text-fig. 20, M., p. 202); and in the tail region it becomes more and 
more closely attached to the ventral surface of the vertebral 
column, projecting merely as a ridge into the cavity of the aorta. 
The ligament itself is a round or oval band of elastic tissue 
forming in the trunk region a thickened edge to a longitudinal 
curtain that divides the cavity of the aorta into two lateral 
channels. 
The ligament is extremely tight, so much so that when the 
trunk muscles are removed, it draws the vertebral column into a 
series of lateral serpentine curves. Its strength is also shown by 
the large size of the elastic ligament between the neural spines. 
In the trunk region the aorta is peculiarly spacious, filling a 
wide channel upon the ventral surface of the vertebral column, 
bounded by the flat lower surface of the vertebral column above 
and by a series of quadrangular heemal arches at the sides and 
below. 
There is little doubt that this ligament is concerned in the 
propulsion of blood within the aorta. ‘The following explanation 
of its action was suggested to me several years ago by the late 
Professor Charles Stewart. 
When a Fish swims, lateral flexions, alternate from side to side, 
pass regularly down the body from head to tail. This is most 
manifest in such Fishes as the Eels and Dogfish, but in com- 
paratively stiff fishes such as the Herrings the action is the same 
although the chief and most powerful flexion takes place when 
the wave of contraction nears the tail. 
It is clear that the aorta will take part in these flexions—a 
swing to either side sweeping in regular sequence from head to 
tail (text-fig. 21, p. 203). 
But the ventral ligament owing to its tension will remain 
practically stationary and will in effect form a series of diagonal 
curtains passing regularly in succession down the length of the 
aorta. Hach curtain will of necessity push the blood before it. 
The faster the fish swims the faster will become the blood 
stream in the aorta. 
This ventral longitudinal ligament is found in, I believe, all 
Proc. Zoou. Soc.—1909, No. XIV. 14 
