256 
Proceedings of the Royal Society of Edinburgh. [Sess. 
the coxa. A fossa, the cor onoid fossa, just distal to the intercondylar ridge 
receives the coronoid boss of the articular spur in extreme extension of 
the basipodite. In extreme flexion the basipodite rests against the medial 
part of the coxal foramen, viz. in the apex of the Cupid’s heart. 
In this way, but by an utterly different, and it may be added less 
efficient, arrangement, great freedom of movement is obtained as in a 
spheroidal bony joint. The mode of union at the essential point, by means 
of a scarcely perceptible groove fitting into the concavity of a hook, is 
mechanically unstable ; thus we explain the existence of supplementary 
arrangements, such as the intercondylar ridge on either side of the inter- 
condylar tubercle, and the great guiding surfaces of the condyles them- 
selves, which play against the bay-walls of the coxal articular foramen 
(the condyles also serve for muscular attachment). 
The articular membrane , covered with soft cuticle, has a proximal and 
a distal line of attachment. On the medial aspect of the articulation, where 
there are no bearing surfaces, it is fixed to the free edge of the segments ; 
at the bearing surfaces it is attached just internal to the smooth parts, 
where the edge again becomes free. In some regions the membrane is 
long and loose, in others short and thickened. In the subjoined table 
•corresponding regions of attachment are set side by side, the general 
nature of the membrane between these regions being also specified. 
Coxal Attachment. 
1 
Basipodal Attachment. 
Nature of Membrane. 
Border of coxal foramen on 
Proximal edge of basipodite 
Large and loose ; stretched 
either side of apex of 
Cupid’s heart 
on medial aspect 
only in extreme exten- 
sion of basipodite 
Summit of anterior bay- 
wall 
Anterior condyle just in- 
ternal to smooth surface 
Loose 
Dorsal aspect of articular 
spur 
Medial free edge of inter- 
condylar ridge 
Short 
Apex of hook on articular 
Free edge of intercondylar 
Strong stout ligament, 
spur 
groove 
which undergoes torsion 
in rotation of basipodite 
Summit of posterior bay- 
wall 
Posterior condyle just in- 
ternal to bearing surface 
Loose 
The muscles are four in number, two flexors and two extensors. When 
the basipodite is forcibly pulled out of the coxal foramen the point of 
insertion of each muscle is rendered plain by the adhering tendon. The 
anterior extensor is inserted into the upper tip of the anterior condyle, 
the 'posterior extensor having a corresponding attachment to the posterior 
condyle — see fig. 4. The anterior flexor is inserted at the base of the 
anterior condyle on its medial aspect ; the posterior flexor is inserted, not 
