THE SKELETON 44] 
fibula. The fibular cartilage extends the entire length of the crus, 
but ossification is confined largely to its proximal end; on the 
fourteenth day its lower half is represented by a thread-like fila- 
ment of bone. 
No separate tarsal elements are found in the adult; but in the 
embryo there are at least three cartilages, 
viz., a fibulare, tibiale and a large distal 
element opposite the three main metatar- 
sals. In the course of development, the 
two proximal elements fuse with one 
another, and with the distal end of the 
tibia. The distal element fuses with 
the three main metatarsals, first with the 
second, then with the fourth, and lastly 
with the third (Johnson). 
Five digits are formed in the mem- 
branous stage of the skeleton. In the 
‘ase of the fifth digit, only a small nodule 
of cartilage (fifth metatarsal) develops and 
soon disappears. The second, third, and 
fourth are the chief digits; the first is 
relatively small. Metatarsals 2, 3, and 4 Fic. 290. — Photograph 
of the skeleton of the 
foot of a chick embryo 
of 15 days’ incubation. 
are long and ossify separately in a peri- 
chondral fashion. They become applied 
near their middle and fuse with one (Preparation and pho- 
another and with the distal tarsal element tograph by Roy L. 
to form the tarso-metatarsus of the adult Moodie.) 
Ne oe OR n : 1, 2,3, 4, First, second 
No 25( st, atarsal is s 5 1) 459545) , Second, 
(Fig. 250). The first metatarsal is short, thied. Ane fourth deite 
lying on the preaxial side of the distal end M2, M 3, M 4, Second, 
of the others (Fig. 249); it ossifies after ee a oe 
the first phalanx. The number of pha- a 
langes is 2, 3, 4, and 5 in the first, second, third, and fourth digits 
respectively (ig. 249). 
The patella is clearly seen in potash preparations of thirteen-day 
chicks. At the same time there is a distinct, though minute, separate 
center of ossification in the tarsal region (Fig. 249). 
