The vertebra is the first part of the skeleton to form however it is still made of cartilage.
The first cartilage that turns into actual bone is the mandible (jaw bone). This Meckel's cartilage turns into bone 3 days before its respective muscles form:
The Meckel's cartilage in human embryonic and early fetal periods."The sequential development of the Meckel's cartilage started as early as stage 13 (32 days) with the appearance of condensation of mesenchymal cells within the mandibular prominence. During stage 17 (41 days), the primary ossification center of the mandible appeared on the inferior margin of the Meckel's cartilage. The muscular attachments to the Meckel's cartilage in embryos were observed at stage 18 (44 days)."
The first formation of actual bones happens at the jaw bone at day 41. Three days later the associated muscles form. This was only known recently. However this was portrayed in the Quran 1400 years before it was discovered.
١٤ ثُمَّ خَلَقْنَا النُّطْفَةَ عَلَقَةً فَخَلَقْنَا الْعَلَقَةَ مُضْغَةً فَخَلَقْنَا الْمُضْغَةَ عِظَامًا فَكَسَوْنَا الْعِظَامَ لَحْمًا ثُمَّ أَنْشَأْنَاهُ خَلْقًا آخَرَ ۚ فَتَبَارَكَ اللَّهُ أَحْسَنُ الْخَالِقِينَ
Bones before muscles, the correct order of formation
How could an illiterate man who lived 1400 years ago have known that bones form before muscles?
The Quran (Koran, the book of Islam) contains scientific knowledge that could not have been known 1400 years ago. It ranges from basic arithmetics to the most advanced topics in astrophysics. You are invited to go through those miracles and judge for yourself.