78 
FOSSIL REPTILTA OF THE 
epiphysis of the Bird’s metatarsus (fig. 4, c) answers to the proximal epiphysis of thei 
Ruminant’s metatarsus (fig. 3, c). 
The interspace between the leg and foot is the seat of variable and inconstant centres 
of ossification, from zero, as in Proteus, Ampliiuma, Aves, to the four ossicles in Orocodilus, 
and the seven ossicles in Chelone. 
The functions of the hind leg in Birds require peculiarly strong, firm, close-fitting, 
interlocking joints. Thus, the fibula articulates directly with the femur, and the meta- 
tarsus as directly with the tibia. No interposed ossicles are permitted to affect the simple 
efficiency of this tibio-metatarsal joint in the long-footed feathered bipeds. In quadrupeds 
and in the short- and broad-footed Bimana tarsal ossicles, interposed at the space b (fig. 
3), have their use. But whether the tarsus exist or not, in the Hamatotherma the articular 
ends of the long bones begin as ‘ epiphyses ;’ and when two or more metacarpals are to 
become massed into one bone, the epiphysis (c) is single — a very significant developmental 
guide to the homology in question. 
The strangest aberrations in homological aims have arisen from a non -recognition of 
the distinction between teleological and homological centres of ossification.^ Not only is 
a tibial epiphysis made into a tarsal bone — and why other epiphyses, such as the proximal 
one of the tibia, or the distal one of the femur, should be differently treated is not obvious — 
but new bones by the score are added to the cranial series. ‘ Basitemporals,’ ‘ prevomers,’ 
" antorbitals,’ ' perpendicular ethmoids,’ ‘ ali-ethmoids,’ &c. &c., have been heaped up to 
obstruct the comprehension of the plain and intelligible nature of the bird’s skull. 
The four unguiculate digits of the foot are of nearly equal length, but present a slight 
difference in their proportions ^ in the Pterosauria. Cuvier having determined the Lacertian 
character of the phalangial formula of these digits, viz. 2, 3, 4, 5, adds that, apparently, 
the .fifth digit was reduced to a slight vestige of two pieces in Pterodactylus lonyirostris? 
Subsequently discovered species have offered a like indication, to which Von Meyer alludes 
as a rudiment or stump (‘ stummel’) of the fifth toe.^ No other specimens, to my know- 
ledge, save the third of Bimorphodm (PI. XVIII) and the Bamphorhynchus (PI. XIX, fig. 5) 
have shown the condition of the fifth digit as of three pieces, viz. a metatarsal [m, v) and 
two phalanges (y, I and 2). 
The metatarsal of this toe shows an interesting affinity to that in the Crocodilia by its 
greater breadth and shortness in comparison to the other metatarsals. The two phalanges 
have proportions and forms which clearly show their adaptive relations as aids in sustaining 
the interfemoral or caudo-femoral parachute (‘Restoration,’ fig. 2, PI. XX). 
1 Owen, “Lectures on the Comp. Anat. of Vertebrate Animals,” 8vo, 1846, p. 38. 
2 See Monograph, pi. xi, fig. 3. 
® “ II paroit qu’ici le cinquieme etoit reduit a un leger vestige de deux pieces.” — ‘ Oss. Foss.,’ vol. 
cit., p. 374. 
^ “Cuvier, Wagler, und Goldfuss lessen den Fuss aus fiinf ausgebilteten Zehen bestehen ; in alien 
Pterodactyln babe ich aber nie mehr als vier soldier Zeben, und bochstens nocb einen Stummel vorgefunden.” 
— Op. cit., p. 20. 
