164 COPE. [Vot. III. 
The fixed articulations are not absolutely without movement, 
because termed fixed. When two adjacent bones become entirely 
motionless through the fixity of their positions, they are apt to 
coossify, especially if growth be stimulated by impact of the 
parts. Such a case is the confluence of the cuboid and navicu- 
lar bones in the Bovidee and Equide, and the fusion of the cunei- 
forms in some of the former. Such are the fusion of the mag- 
num and unciform in the manus of the Cycloturus, and of the 
trapezoides and magnum in Bradypus. Such the union of the 
metapodials in both extremities of the three-toed sloth. The 
fusion of the scaphoid and lunar bones in the Carnivora is not so 
readily explained. It may be, however, traced toa strain similar 
to that experienced by the feet of sloths, Cycloturus, etc., but for 
a different purpose, that of seizing and rending prey. But this 
suggestion may be worthless, and it does not offer any demon- 
stration as to how such strains should produce such result. 
The fixed articulations are those between the carpal and tarsal 
bones, and those between these and the metapodials. In the 
Diplarthra another fixed articulation is that between the ulna 
and radius, and in this and other orders, that between the tibia 
and fibula. 
a. The Ulna and Radius. 
The relation of the head of the radius to the ulna is, in lower 
land vertebrates, a more or less loose one. In the lower Mam- 
malia the head is generally oval, permitting of greater or less 
supination of the manus. In the higher Edentata and Taxeo- 
poda, the head becomes round, permitting perfect supination in 
the great anteater, the monkeys, and man. In the Ungulata its 
development is in the opposite direction or towards fixity. It 
becomes flatter, and incapable of movement ; and, finally, in the 
Artiodactyla, it is firmly articulated with the ulna by a coarse 
peg and notch, or gomphosis, followed by coossification in the 
Camelidz. It is evident that the rotundity of the bead of the 
radius has been produced by the more or less successful attempt 
to’ rotate it in the act of supinating the manus. The immovable 
condition seen in the Ungulata is as clearly due to disuse of the 
supinating function, in a use of the fore limb where such move- 
ment is unnecessary. It appears that the impact or concussion 
of the blow of the ungulate foot on the ground has caused an 
