The anterior fontanelle was opened and radiolucent in the second trimester; at the third trimester, the fontanelle began to shrink and finally closed at birth and became radiopaque. The borders of the orbit and the teeth were both radiolucent and undifferentiated at the second trimester and at the third trimester, and these regions became radiopaque at the second and third trimester, respectively. The histomorphology of the calvarium in the first-trimester foetus had three layers consisting of the mesenchymal and osteoblast cells; as the foetus ages within the second trimester, the mesenchymal cells were transformed into osteoblast, colonies, primitive bone spicules, matured bone spicules, and primitive trabeculae respective, in the third trimester, the primitive trabeculae developed into a matured trabeculae, in the day old, the matured trabeculae transforms into a primitive spongy bone. However, this process occurs earlier in Yankasa than in Uda. The histomorphology of the calvarium during foetal life is similar in the Uda and Yankasa. However, the stages of calvarium development occur earlier and faster in Yankasa than Uda of the same ages. This implies that foetal development and time of parturition could occur earlier in the Yankasa compared to the Uda breeds.
Key words: Anterior fontanelle, Calvarium, Osteoblast, Radiopaque, Skull