ARTICULATIONS OF THE BONES. 115 
this case is limited by the dimensions of the intervening 
cartilage, sometimes by its nature; for, where it serves to 
connect the vertebra of quadrupeds, it is much more flex- 
ible and elastic than it is in the other parts. Where two 
bones are united, by the intervention of ligament, or even 
skin, the junction may be termed Syndesmosis, (cuvdeopeos li- 
gamentum.) It is harmonic when the even edges of thin 
bones are prevented from coming in contact, or from reced- 
ing, by the intervening soft part. In this case, the extent 
of motion is limited by the degree of flexion or extension 
of which the connecting medium is susceptible. The shells 
of the Bernacle (Lepas) afford good examples of this kind of 
connection. Inthe squamous syndesmosis, thethm edgeof one 
bone covers the surface of another, in such a manner as to 
permit both bones to slide upon each other. The gill-flaps 
of many fishes, some of the bones of the head of the lamprey, 
and the dorsal plates of the chifons exhibit this kind of arti- 
culation. In the syndesmosis, by inclusion, the bones or hard 
parts are in the form of tubes, united to each other at the 
extremities by a common membrane passing from the one 
to the other. When the common membrane is leng, flexi- 
ble, and elastic, almest every kind of motion may be per- 
formed. When the tubes are nearly in contact, a lateral 
movement only can be executed, by a part of the cireumfe- 
rence of the one tube penetrating the interior of the other. 
When the one tube is smaller than the other, it may be 
withdrawn into the cavity of the larger, or extended, at the 
will of the animal. There are frequently processes and ca- 
vities in the contiguous margins of the tubes, which regu- 
late the direction and extent of the motion this kind of 
junction is designed to perform. Numerous examples of 
articulation by inclusion, occur in the limbs of insects and 
crabs. 
H 2 
