The maxillary sinuses are very large in the Elephant, and are divided into numerous inter communicating cells which open into the side of the nose by a wide orifice. In•the flog tribe these sinuses do not exist, but in their stead their is a cavity in the malar bone, which in the Ethiopic Boar is very large. A similar cavity of smaller size exists in the Hippopo tamus.
The sphenoidal sinuses are very small except in the Elephant, in which, like the preceding, they are of unusual dimensions, extending even into the pterygoid processes ; .but they are not divided into cells as are the other sinuses of this creature.
Eye.—The optic apparatus requires but a few passing observations.
The external boundary of the orbit is com pleted by a strong ligamentous margin.
The third eyelid is very largely developed in the Elephant, and can be drawn over the eye ball to a considerable distance towards the outer angle of the eye. It is provided in this animal with two special muscles which do not exist in other quadrupeds. One of these, which seems to draw the nictitating membrane over the eye-ball, arises from the lower margin of the orbit, towards the outer canthus; while the other, which is the antagonist of the former, draws it back again towards the inner angle.
The lIarderian gland is of very great size, and opens by a capacious duct upon the inner surface and close to the base of the third eyelid ; in some species, however, as in the Elephant, numerous small accessory glands are met with, the excretory orifices of which terminate near the margin of the nictitating membrane. The
nictitating membrane itself is very large, and sometimes contains a flat, thin, and slightly curved cartilage. Moreover, in the Elephant especially this membrane really deserves to be considered as a proper eyelid, being moved by a distinct muscle, the nictitator, the fibres of which pass in a regular curve over the base of the membrane, but afterwards deviate from the curve and form an angle to include the ex tremity of the nictitating cartilage, which con sequently moves in the diagonal of the con tracting forces so as to be drawn outwards over the front of the eyeball.
Ligamentam ?whey. — The ligamentum nuch is of enormous strength, more especially in the larger Pachydermata, such as the Ele phant and Rhinoceros, where the ponderous head necessarily requires unusual support.
In the American Tapir this ligament consists of three strong portions, two of wh ich pass in a pa rallel direction from the elongated spinous pro cess of the first dorsal vertebrx, to be inserted together into the superior and posterior angle of the central ridge of the craniurn supporting the whole length of the elevated crest and mane; the third portion runs beneath the other two, to be inserted into the most elevated part of the elong,ated spinous process of the vertebra den tata.