Number of somites developed in human fetus -

Ans. is 'd' i.e.,42 pairs o Paraxial mesoderm differentiates into somites.o By the end of 20th day, the first pair of somites have formed in neck region.o After this, about 3 pairs of somites are formed per day and by the end of 5th week about 42-44 somite pairs are formed (4-occipital, 8-cervical, 12-thoracic, 5-lumbar, 5-sacral and 8-10 cooccygeal).o Somites are further differentiated intoi) Dermatomyotome :- Give rise to skeletal muscles and dermis.ii) Sclerotomes Give rise to vertebral column and ribs.