Achondroplasia is an

autosomal dominant disease that leads to a disorder of endochondral

ossification. A typical picture is a disproportionate growth disorder. However,

the trunk is almost normal length, the limbs are very short. Another feature is

a brachycephalic skull (pear-shaped), a broad forehead, and supraorbital

arches. Which type of cartilage is the model for the newly formed bone?