1052 
ME. J. W. HULKE ON THE OSTEOLOGY 
fibula which here lies upon it. The axis of the shaft is twisted in such a manner that 
a plane laid through the long diameter of the proximal end cuts at a large angle 
another plane laid through the long axis of the distal end (Plate 80, fig. 8). 
The following are some of the dimensions of a fully grown tibia :—Extreme length, 
22-25 centims. ; breadth across the proximal condyle, 3‘35 centims.; from the back of 
the inner condyle to the most prominent point of the prmcnemial crest, 5 *7 centims.; 
breadth across the malleoli, about 4*6 centims. 
Fibula (Plate 77; Plate 78; Plate 81).—The upper end is flattened. It rests 
against the outer surface of the outer proximal condyle of the tibia behind the great 
prsecnemial crest. In flexion of the knee it is received in a groove on the outer 
femoral condyle, as already mentioned. The shaft, sub-prismatic, rests in its lower half 
on the anterior surface of the tibia, just within its outer border. Its distal end is stout. 
It articulates with the anterior of the two divisions in the upper surface of the os colds. 
^ >es ' The tarsus comprises two distinct bones corresponding to those of the 
proximal row of ossa tarsalia of other Vertebrates—an os tibiale or astragalus , and an 
os Jibulare or ca Ids. Evidence of the presence and the composition of a distal row of 
distinct tarsalia is yet ^incomplete. 
Astragalus (Plate 80, figs. 3-7).—The upper surface of this, the largest tarsal 
bone, is the counterpart of that of the tibia; it is concave from front to back, and in 
this direction divided by a ridge that marks out two portions corresponding to the 
inner and part of the outer tibial malleolus. The under surface is pulley-shaped, 
convex from front to back, and sinuous transversely, being in this direction convex 
towards the ends and concave intermediately. The anterior margin is a thin lip, the 
posterior margin is stout. The inner end is non-articular and sub-cutaneous, the outer 
end (very thin by the approximation of the upper and under surface) articulates with 
the os calds. 
Os calds (Plate 80, figs. 3—7).—The outer, non-articular, sub-cutaneous surface is 
crescentic. The upper border, nearly straight, is interrupted by a slight elevation, 
the outer end of a ridge which divides the upper surface into an anterior moiety that 
receives the end of the fibula, and a posterior in which the outer part of the external 
tibial malleolus rests. The under surface is convex from front to back. The inner 
surface, or rather border, very narrow, articulates with the astragalus. 
The astragalus and os colds conjointly form a pulley-shaped articular surface on 
which the front part of the pes moves. The interlocking of the upper surface of the 
conjoined bones with the ends of the tibia and fibula renders impossible any movement 
of them upon the leg-bones. 
In a right foot of a nearly fully-grown Hypsilophodon I found a wedge-shaped bone 
inserted between the proximal end of the IVth. metatarsal and the os calds. Its 
position and shape correspond to a bone in the pes of Scelidosaurus Harrisonii* and 
Owen, E., “British Fossil Eeptilia of the Oolitic Formation,” part ii., plate x., fig. 1. 
