Figure S1.

Sphenoid development in human embryos and fetus, related to Figure 1

(A–I) 3D reconstructions of chondrogenic markers immunolabeling at PCW5.6 (Sox9; A–D), PCW7.0 (Collagen 2; E–G) and PCW11.3 (Sox9; H and I), showing progressive assembly of nasal capsule (blue, 10–15), sphenoidal (green, 20–28), occipital (orange, 30–33), and petrosal (yellow, 40–45) chondrogenic templates of the skull base.

(A–C) The nasal capsule develops remotely, anteriorly from the other three structures, which are already in close proximity at PCW5.6, as seen from superior (A), frontal (B), and lateral (C) views. The isolated sphenoid is a single mass, the basisphenoid (20) flanked by two independent ventro-lateral masses, the ala temporalis (22).

(D) A weak Sox9 labeling delineates the trigeminal nerve, or fifth cranial nerve (CNV) , confirmed on section. This shows the passage of the maxillary (CNV2, 52) trigeminal branch through central holes of the ala temporalis (22), prefiguring the foramen rotundum (54). In contrast, other branches (CNV1, 51, and CNV3, 53, traced from the Gasserian ganglion, 50) run outside of this structure.

(E–G) At PCW7.0 (E, supero-dorsal view; G, lateral view; F, superior close up of the nasal capsule showing the superior surface of the initial basiphenoid (20 in A), which will develop as the main sphenoid body in the adult, splits posteriorly into the sella turcica (21) and anteriorly into the presumptive planum sphenoidale (28). Laterally, the orbitosphenoids (23) that have formed and expanded are connected to the basisphenoid (20 in A), prefiguring the sphenoid lesser wings (23). Likewise, connected to the basisphenoid (20), the alar processes (24) connect to the ala temporalis (22) as the presumptive greater wings. Frontal spheno-ethmoidal cartilage interfaces (15) prefigure the dorsal domain of the orbit. The dorsum sellae (25) rises dorsally, flanked laterally by the posterior clinoid processes (26). A depression of the cartilage plate can be observed as the future hypophyseal fossa or sella turcica (21). The parietal lamina (or plate, delimited by the dotted line) was identified (G and I).

(H and I) Interestingly, the pterygoid plates were not visible (while the pterygoid muscles were present). At PCW11.3 (H, superior view; I, lateral view), two large lateral holes prefigure the superior orbital fissures (55), along with other foramens (45, internal auditory canal; 58, hypoglossal canal; 59, foramen magnum).

The bottom table lists all individual anatomical structures annotated on the figure.

Scale bars: 500 μm in (A)–(D), (F), and (G); 1 mm in (E); and 1.5 mm in (H) and (I).