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Development of Limbs (cont)

Each bud consistsof a mass ofmesenchyme

covered byectoderm.

Ectoderm at the

distal border of thelimb bud thickens toform an apicalectodermal ridge(AER).

Week 5

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Development of Limbs (cont)

Mesenchymal cells further from AER begins to differentiate to cartilageand muscles.

Development proceed proximodistally.

The distal ends of limb buds flatten into paddle-like hand or foot plates.

A circular constriction separates the hand or foot plate from the

proximal segment which will form the rest of the limb.

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Development of Limbs (cont)

A 2nd constriction

divides the proximal

segment into 2 parts

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Development of fingers and toes

Cell death occurs atthe AER dividing theridge into 5 parts.

Condensation ofmesenchyme formcatilaginous digital

rays

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Development of upper & lower limb

At wk 6--------------thefirst hyaline

cartilagenous model

appear.

complete set ofcartilage model at the

end of week 6 --- the

beginning of week 8.

Development of lowerlimb is 1-2 days behind

that of the upper limb

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Ossification of bone of limb

Condensation of

mesenchyme forming

cartilage model (week 6).

Endochondral ossificationstarts the end of week 8.

Ossification centre appear

in all long bones by the end

of week 12.

D= at birth all the shafts are

ossified + all epiphyses are

cartilage.

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Development of Limbs (cont)

Muscles of limbs

develop from the

mesenchyme

surrounding the

developing bones.

Ventral rami of spinal

nerves invade the limb

buds (C4-T2) for upper

limb & (T12- S4) for

lower limb.

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Rotation of Limbs

At week 7 the upper & lower

limbs rotate .

Upper limb rotates 90

laterally extensors lie

posterior (elbow points

posterioly) & thumb lies

lateral.

Lower limb rotates 90

medially extensors lieanterior (knee points

anteriorly) & big toe lies

medial.

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LIMB ANOMALIES (cont)

Amelia completeabsence of a limbor limbs.

Meromelia partialabsence of limb or

limbs

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Cleft hand & cleft foot

(lobester claw deformity) cleft between 2nd

and 4th metatarsalsand soft tissue.

Absence of thecentral digit (3rd) +fusion of peripheraltoes.

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Brachydactyly

short digitsresulting from

defectivedevelopment ofphalanges(heriditary )

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Polydactyly

presence of an extradigit.

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Syndactyly = abnormal fusion due tofailure of the webs to degenerate

between 2 or more digits

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Congenital Club Foot (Talipes)

The commonest is talipesequinovarus where the footis inverted, with the solefacing medially

( more common in males).

Caused by abnormalposition of legs in utero.

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