THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 



173 



piece of cartilage which corresponds to the navicular (scaphoid). Ossification 

 begins relatively late in the metatarsals. A center for the calcaneus appears 

 during the sixth month of fcetal life, and one for the talus shortly before birth. 

 Centers appear in the cuboid and third cuneiform during the first year after 

 birth, and in the first cuneiform, navicular and second cuneiform in order during 

 the third and fourth years (Figs. 150 and 151). At the age of puberty ossifica- 

 tion is nearly complete in all the metatarsals. In the talus two centers, cor- 

 responding to the tibial and intermedial, appear, but soon fuse into a single 

 center. Occasionally the intermedial remains separate and forms the trigonum. 



Calcaneus ~ 



FIG. 150. Ossification centers in foot of a child 9 months old. Hasselwander. 



An accessory center appears in the calcaneus at the insertion of the tendon of 

 Achilles. 



; The metatarsals and phalanges develop in a manner corresponding to the 

 metacarpals and phalanges (of fingers). Ossification begins in the metatarsals 

 about the ninth week, in the first row of (proximal) phalanges about the 

 thirteenth week, in the second row about the sixteenth week and in the third 

 row (distal) about the beginning of the ninth week. Epiphyseal centers ap- 

 pear from the second to the eighth year after birth. 



Development of Joints. 



The embryonic connective tissue from which the connective tissues, includ- 

 ing cartilage and bone, are developed, at first forms a continuous mass. When 

 cartilage appears it may form a continuous mass, as in the chondrocranium, or 



