102 
Proceedings of the 
municating across the mesial plane behind the ligament. In the 
horse there are not only two synovial membranes for the head of 
each rib, but an intermediate one for the ligament itself. 
In the rabbit, fibres extend across from the head of one rib to that 
of the opposite, but are closely incorporated with the intervertebral 
disc. 
In the kangaroo, monkey, and human subject, there is no trace 
of the transverse intercostal ligament. 
The author is inclined to consider this transverse intercostal liga- 
ment as represented by the transverse ligament of the atlas, and both 
structures as morphologically related to the perforated form of the in- 
tervertebral disc. 
The communication concluded with observations on the relative 
movements of the ribs and spine, in connection with this ligament ; 
and on its probable functions. 
4. On the Movements of the Articulation of the Lower Jaw. 
By Dr John Smith. Communicated by Professor Goodsir. 
After alluding to the difficulty of determining the precise anato- 
mical configuration of the condoles of the lower jaw, especially in 
the human subject, the temporo-maxillary articulation admitting of 
a multiplicity of movements, and these again being liable to modifi- 
cation by different accidental and other conditions of relative struc- 
tures, such as the teeth, &c., the author stated that a general prin- 
ciple would nevertheless be found to prevail, and in general to be 
distinctly traceable in this joint, whatever might be the modifications 
existing either in its function or external form. 
In man, and many of the mammalia, one essential movement of 
the lower jaw consists in simply opening and shutting the mouth, in 
a vertical plane : here the temporo-maxillary articulation is said to 
act as a simple hinge. Another essential motion is that by which 
grinding of substances between the molar teeth during mastication 
is performed : here the action of the joint has apparently been 
regarded as somewhat irregular and subordinate in its nature. 
In the first-mentioned movement, however, the condyles cannot 
act as a simple hinge, as they lie — not at right angles to the plane 
of motion of the lower jaw — but obliquely to it, each condyle looking 
inwards and forwards. Their more perfect action, therefore, cannot 
