Figure 3.

Development of the human oculomotor system

All panels are LSFM images of solvent-cleared embryos (A–H) and fetuses (I–N) immunostained with anti-MHC combined with ChAT (A–F, K, and L) or synaptophysin (G–J, M, and N). For each specimen, the upper panel corresponds to the merge image of the motor nerves and oculomotor muscle and the lower panel to the nerves. The inset on the left upper side of the figure provides the color code for muscles and nerves.

(A and B) At PCW5.6, only 4 muscles are visible. All muscles are innervated except the superior oblique (arrow).

(C and D) At PCW6, the 6 extraocular muscles, including the medial rectus (arrowhead) and inferior oblique (arrow) are now present and innervated.

(E and F) This is similar at PCW7.

(G and H) At PCW8.4, the levator palpebrae starts to split from the superior rectus (arrow in G) and receives a small branch coming from the oculomotor nerve (arrow in H). Note the expansion of the inferior oblique.

(I–K) Between PCW9.5 (I and J) and PCW10.4 (K and L), the size of the levator increases and it detaches completely from the superior oblique.

(M and N) At PCW11.3, the terminal branches of the nerves occupy the central part of all muscles and display a large bouquet of synaptophysin+ endplates. Abbreviations are as follows: III, oculomotor nerve; IV: trochlear nerve; and VI, abducens nerve.

See also Figure S4.

Scale bars: 500 μm in (A)–(M).