MOEPHOLOGT OF THE GALLINACE.E. 235 



for it shows a small bud at the top of the intermedium (i.), which bud is the remnant of 

 the long band, so well seen in many other birds, whilst the Fowl is very ornithoscelidan 

 in the greater arrest of this part. 



Both this and the last stage (figs. 13, 14, and 10-12) show the structure and relations 

 of the massive scaphoid, or centrale — a part continuous with, and formed out of, the 

 massive interarticular plate; no "sesamoid "or even " calcaneum " is this great cres- 

 centic wedge of solid hyaline cartilage ! The single distal tarsal ossification (figs. 13, 14, 

 dt.) is seen most in front, under the intercondyloid peg (fig. 14, c.) ; but it shines 

 through the sides of the cartilaginous mass (fig. 13), having given off side-growths of 

 bony matter that represent the 2nd and 4th distal tarsals of a normal Reptilian ankle- 

 joint. At this late date, in chickens the size of a Quail, the tibia has not yet coalesced 

 with the proximal tarsal mass ; its tendon-bridge (t.br.) is still soft. 



The Sth stage, in young Fowls of the first summer, yields the same instructive facts. 

 In a young Cock, four months old, the spur (fig. 18, spr.) is still very little developed 

 outwards. Looked at in the light of general Morphology, we see that this is a solid 

 fibro-cartilage ; and its position and relations proclaim it to be a veritable " pre-hallux." 

 If the spur of a Fowl were merely a spinous, horny scale, its solid core corresponding 

 with the dermal scutes of Ci/clodus, Scincus, Anguis, or of the Crocodilia, then there 

 would have been no fibro-cartilage developed. But that special tissue, just one degree 

 lower in the scale than hyaline cartilage, when it is developed, has always some direct 

 morphological meaning ; it is no longer a mere tract ; it becomes an elem ent of the 

 skeleton. It was evident at the end of 10 days' incubation (Plate XXIV. fig. 4, spr.) ; and 

 in the Purple Pheasant {Euplocamus Horsfieldii), near the time of hatching (Plate XXVI. 

 fig. 20), it is seen as a considerable disk a little way above the semi-osseous distal 1st 

 metatarsal (mt. 1 ), as in the Fowl. In the latter (fig. 18) it has raised itself so as to form a 

 hemispherical bud, and the once flat scale has now become like a deep watch-glass. 



Later in the season, in young Fowls 7 or 8 months old, there is much soldering to be 

 done before the strong ankle-joint is complete. At this stage(Plate XXIV.figs. 15,16) there 

 appear to be several epiphyses in the hind limb and two large sesamoids ; and nothing but 

 a complete history of the development of these parts is sufficient to correct this first view. 

 There is a sesamoid, the patella (pt.), at the knee-joint, and directly below it an epiphysis, 

 or the cnemial process (cn.e.). But at the ankle-joint the apparent sesamoid is the scaphoid 

 or centrale (c), and the apparent epiphyses are the proximal and distal tarsal masses — 

 the upper being the tibiale and fibulare united together, and also to the intermedium in 

 front of and above them ; and the lower mass is the distal tarsal common to the 2nd, 

 3rd, and 4th metatarsals ; this mass has developed a huge continuous outgrowth for the 

 plantar tendons *. 



In the adult (figs. 17 and 19) the outer and inner ridges of that outgrowth have been 

 formed into a canal by periosteal growths, and the scaphoid is seen as a strong sub- 

 trihedral, somewhat curved bone, which plays upon the back of the region of the tibiale, 

 behind the inner side of the joint. 



* This is the stage in -which the Fowl has been compared to the Iguanodon by Prof. Huxley (see Proc. Geol. Soc. 

 Nov. 10, 1869, pp. 12-31). 



