Fig. 4. Human head injected with blue latex (no. 7): sagittal section passing through the eyeball and the optic nerve. (A ) Left orbit injected with 4 ml into the intraconal space via  an inferotemporal approach (retrobulbar anesthesia). (B ) Right orbit injected with 6 ml of latex via  the superonasal quadrant of the extraconal space (peribulbar anesthesia). (A ’ and B ’) (Semischematic view of A  and B  with the superimposed place where the intermuscular membrane should be (dotted line). 1 = optic nerve; 2 = inferior rectus muscle; 3 = superior rectus muscle–levator palpebrae superioris muscle complex; 4 = lateral rectus muscle (cross-sectioned). Note the spread of latex from one space to the other, through the supposed intermuscular membrane, resulting in a very similar picture after both injections.