The next layer is the where the existing, columnar chondrocytes enlarge and thus force the separations between lacunae to become very thin.
. (a)-zone of cell proliferation
(b)- zone of hypertrophy
(c)- zone of calcification
(d)- zone of deposition

(b)- zone of hypertrophy

Explanation:

Hypertrophic cells synthesize alkaline phosphatase by calcifying the surrounding area; prevent the diffusion of substances, this causes chondrocyte death; therefore, the matrix degrades and the lagoons converge, then the blood vessels proliferate in the collarete to vascularize the cavity. The primitive periodic cells migrate to the vascular borders to become osteoprogenitor cells which are attached to the cartilaginous spicules leaving the degradation of the calcified cartilage, then they become osteoblasts. The combination of cartilage and bone matrix forms a mixed spicule.

Endochondral bone growth begins in the second trimester of fetal life and goes to adulthood, in it there is presence of epiphyseal cartilage.

The epiphyseal cartilage has several areas including:

Hypertrophy zone: it is composed of large chondrocytes that accumulate glycogen. The matrix is compressed between the hypertrophied cartilaginous columns.