 one of them according to its texture. some of them are very hard such as the sphenoid bone and some of them are very soft compared to the rest of the bones such as the fontanelle bones especially the front ones. and some of them are in between these two parts such as the bones of the hands and feet.
أحدها بحسب قوامها. فإن منها ما هو شديد الصلابة كالعظم الوتدي، ومنها ما هو شديد اللين بالنسبة إلى باقي العظام كعظام اليافوخ خاصة مقدمه. ومنها ما هو متوسط بين هذين القسمين كعظام اليدين والرجلين.