This week your baby weighs a little over 4 pounds and has passed the 17 inch mark. He's rapidly losing that wrinkled, alien look and his skeleton is hardening. The bones in his skull aren't fused together, which allows them to move and slightly overlap, thus making it easier for him to fit through the birth canal. (The pressure on the head during birth is so intense that many babies are born with a cone-head like appearance.) These bones don't entirely fuse until early adulthood, so they can grow as his brain and other tissue expands during infancy and childhood.