500 BRITISH FOSSIL REPTILES. 



epiphysis of the Bird's metatarsus (fig. 4, c) answers to the proximal epiphysis of the 

 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, Amphiuma, Aves, to the four ossicles in Crocodilus, 

 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 femvn-, 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 Hcematotherma 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 bu'd'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 Pterodadylm longirostris? 

 Subsequently discovered species have offered a like indication, to which Von Meyer alkides 

 as a rudiment or stump (' stummel ') of the fifth toe.^ No other specimens, to my know- 

 ledge, save the third of Dimorpliodon (PI. 16) and the Bhavqihorhynclms Meyeri (p. 502), 

 have shown the condition of the fifth digit as of three pieces, viz. a metatarsal (w, v) and 

 two phalanges (y, 1 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. 17). 



^ Owen, "Lectures on the Comp. Anat. of Vertebrate Animals," 8vo, 1846, p. 38. 



- " II paroit qu'ici le cinquieme eloit reduit a im leger vestige de deux pieces." — ' Oss. Foss.,' vol. 

 cit., p. 374. 



* "Cuvier, Wagler, und Goldfuss lassen den Fuss aus fiinf ausgebilteten Zehen bestehen ; in alien 

 Pterodactyln liabe ichaber uie niehr alsvier solcherZelKii, unJbocbstens nocli einen Stummel vorgefunden."' 

 ,— Op. cit., p. 20. 



