ORGANS OF SENSE.
Eye.—The eyeballs are of large size, and well developed at birth. The pupil is closed by a vascular membrane called the membrana pupillaris, which disappears at about the seventh month. Sometimes it remains permanently, and produces blindness. It consists of two thin membranous layers, between which the ciliary arteries are prolonged from the edge of the iris, and form arches and loops by returning to it again, without anastomosing with those of the opposite side.
The removal of the membrane takes place by the contraction of these arches and loops toward the edge of the pupil. The capsule of the lens is extremely vascular.
Ear.—The ear is remarkable for its early development; the labyrinth and ossicula auditus are ossified at an early period, and the latter are completely formed before birth. The only parts remaining incomplete are the mastoid cells, and the meatus auditorius. The membrana tympani in the fetal head is very oblique, occupying almost the basilar surface of the skull; hence, probably, arises a deficient acuteness in the perception of sound. It is also extremely vascular.
Nose.—The sense of smell is imperfect in the infant, as may be inferred from the small capacity of the nasal fossæ, and the non-development of the ethmoid, sphenoid, frontal, and maxillary sinuses.