Embryology
Clothed in Flesh
Scientific Context
Development of the Skeletal Scaffold
The human skeletal system is built in two passes. The first pass produces a complete cartilaginous framework — a working miniature of the adult skeleton, recognisable as a skeleton, in place by the sixth or seventh week of development. The second pass produces the muscles that will move it. The two passes do not happen at the same time, and the first pass is finished before the second one begins.
In the first step, a cartilaginous skeleton forms through a process called chondrogenesis. Mesenchymal cells condense in the regions where bones will eventually be and differentiate into chondrocytes, the cells that secrete cartilage matrix. By the fifth week, cartilage models are present for nearly every bone in the body — the long bones of the limbs, the bones of the hands and feet, the vertebrae, the ribs. By the end of the sixth week, the cartilage model of each bone is in place. From the seventh week onward, ossification begins: blood vessels invade the centre of each model, osteoblasts arrive, and the cartilage is gradually replaced by mineralised bone.
In the second step, skeletal muscle appears and is laid down around the framework from the outside. The precursor cells of muscle — myoblasts — are present from early in the embryonic period, but they only begin to fuse into multinucleated muscle fibres in the seventh and eighth weeks, after the cartilage skeleton is already in place. The fibres then migrate, attach to the skeletal elements through tendons, and organise into the muscles that will move the limbs. The order is invisible in the finished body, where bone and muscle meet in seamless contact, and was established only through the serial-section work of nineteenth- and twentieth-century embryology — most famously the Carnegie collection at the Johns Hopkins Anatomical Laboratory, assembled under Franklin Mall, and the staging system derived from it by George Streeter in the 1940s and 1950s.
Islamic Context
ثُمَّ خَلَقْنَا النُّطْفَةَ عَلَقَةً فَخَلَقْنَا الْعَلَقَةَ مُضْغَةً فَخَلَقْنَا الْمُضْغَةَ عِظَامًا فَكَسَوْنَا الْعِظَامَ لَحْمًا
Then We made the (sperm) drop into a clinging clot, and We made the clot into a lump, and We made the lump into bones, and We clothed the bones with flesh.
— Quran 23:14
The verse moves through four transformations. The first three are introduced by a form of the verb khalaqa — to make, to bring into being: fa-khalaqnā the drop a clinging clot, fa-khalaqnā the clot a lump, fa-khalaqnā the lump bones. The fourth breaks the pattern. It does not say fa-khalaqnā. It says fa-kasawnā — and the shift in verb is the verse's own signal that the final step is a different kind of act from the three that preceded it. The three earlier steps describe the bringing of a thing into existence. The fourth step describes an action that is being done to something that already exists.
Kasā, in the classical Arabic lexicon, is the verb for clothing. The root of the word carries the image of an outer thing laid over an inner thing that already has its own existence: a body put into clothes, a covering drawn across a frame. Ibn ʿAbbās (d. 687) read fa-kasawnā al-ʿiẓām laḥm as a literal description: the flesh grows over the bones the way a garment is wrapped over a body, with the bones as the support and the flesh as what covers them. Al-Rāzī (d. 1210) takes the reading further. The choice of kasā over khalaqa at this point is deliberate, because the bones have already been brought into being by the verb of creation, and what is happening to them now is not creation but covering. The verb has changed because the act has changed.
Ibn ʿĀshūr (d. 1973), in al-Taḥrīr wa al-Tanwīr, takes the sequence as hierarchical — each of the four stages builds on what the previous one established, and the final stage presupposes the existence of the bones as a complete framework before anything is wrapped around them. Unlike the first three stages that each name only one thing, the final stage names two things, bone and flesh, in that order. The grammar inherent in the Arabic does not say that bones and flesh appear together. It does not say that flesh is made and bone is generated within it. It says bone is made first and then clothed in flesh.
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The Connection
The Qur’an details a four-stage process where bones are brought into existence before being clothed in flesh. This matches the timeline of human development: the cartilaginous skeleton is established as a complete framework before muscle fibers are recruited to cover it. The verb used for this final stage, kasawnā (clothing), accurately describes the process of wrapping an external layer over an existing form. The text not only lists the stages of growth but correctly specifies the order and the nature of the development.
