MLV drainage from the rostral CAV. (A) Schematic of veins of the ventral forebrain and olfactory bulbs (OB). (B–O) Dashed lines indicate the level of coronal sections shown in B–O, and lymphatics are numbered 4–6. Black circles, optic nerve foramen (of); anterior lacerated foramen (alf). abv, anterior basal vein; iophv, internal ophthalmic vein; IOS, inferior olfactory sinus; olfev, olfactory emissary vein; ON, optic nerve (yellow); ophev, ophthalmic emissary vein; RCS, rostral confluence of sinuses; rrhv, rostro-rhinal vein; SOS, superior olfactory sinus. (B) vWF⁺ veins (blue) and tracer deposits (OVA-A⁵⁵⁵, magenta) in the iophv perivenous area and around the ophev at lymphatic uptake site 4. Dotted line, skull border. (C–G) LYVE1⁺ MLVs (green) and OVA-A⁵⁵⁵ (magenta) around the CAV at level 4 (green arrowheads). Th-Lb (B–F) or ICM (G) injections of OVA-A⁵⁵⁵ were performed 45 min before sacrifice. MLVs contact perisinusal OVA-A⁵⁵⁵ deposits (C). (D) Magnification of dotted frame in C. OVA-A⁵⁵⁵ is present within MLVs (white arrowheads). (E and F) Coronal (E) and sagittal (F) views of MLVs following the ophev toward the orbital cavity (orange arrows) and connecting ventrally to lymphatics of the nasopharynx (NP, white arrows). (G) Note similar labeling pattern to C; MLVs exit the skull through the alf and prolong along the ophev toward the orbital cavity. (H–K) Meningeal veins (vWF⁺, blue in H), lymphatic vasculature (LYVE1⁺, green in I–K), and tracer deposits (OVA-A⁵⁵⁵, magenta) on coronal (H–J) and sagittal (K) views at section level 5. (H) Tracer accumulated around the confluence of the olfev with the CAV (blue arrowheads). Stippled area, alf. (I–K) LYVE1⁺ MLVs follow the olfev to exit the skull toward the orbital cavity (orange arrows) and extend ventrally toward the NP (white arrows). OVA-A⁵⁵⁵ deposits were found in LYVE1⁺ MLVs (insets in I). Coronal (J) and sagittal (K) view of the orbital cavity. MLVs exit the skull toward the orbital cavity (orange arrows) and the NP (white arrows). (L–O) Rostral end of CAV at section level 6. (L) Tracer accumulated around the confluence of the IOS with the CAV (blue arrowheads). Green arrowheads, MLVs at the rostral end of CAV take up tracer (white in M). MLVs extend rostrally from the CAV along the IOS on the lateral side of each olfactory bulb (N and O, blue arrowhead). OE, olfactory epithelium. (P–S) Horizontal (P and Q) and sagittal (R and S) views of the anterior part of the head showing the IOS, SOS, and RCS. Dural veins (vWF⁺, blue in P), lymphatic vasculature (LYVE1⁺, green in Q–S), and tracer deposits (OVA-A⁵⁵⁵, magenta). (Q) MLVs connect the CAV with the RCS via the IOS and SOS. (R and S) OVA-A⁵⁵⁵ is accumulated around MLVs at the SOS (Q and R) and RCS (R and S) Scale bar: 300 μm (C–S).