Limb Buds

Lower limb buds bulge from the lateral aspect of which segments of the trunk ?

a. C5-T1

b. T7-L2

c. L1-S5

d. L2-S2

ANSWER:

Ans: D
The upper and lower limbs develop from limb buds that arise from the lateral body wall during the 4th and 5th weeks, respectively.
Upper limb -> C5 - T1 segments.
During the 5th week, lower limb buds bulge from the lateral aspect of the L2 - S2 segments of the trunk.
Also, during the seventh week of gestation the limbs rotate in opposite directions. The upper limb rotates 90◦ laterally, so that the extensor muscles lie on the lateral and posterior surface and the thumbs lie laterally, whereas the lower limb rotates approximately 90◦ medially, placing the extensor muscles on the anterior surface and the big toe medially.