The optic nerve approaching the sclerotic coat becomes altered into a conical extremity, which enters a sheath and is directed downward and obliquely forward. The extremity of the optic nerve in the interior of the eye presents a white narrow streak. Branches of the opthalmic artery enter the eye between the lamina of the retina, along the whole extent of the oblique slit, and penetrate the fold of the pecten upon which they form a delicate ramification. The crystalline lens is of soft texture. It is inclosed in a capsule and is nearly round. It adheres very firmly in the depression in the anterior part of the vitreous humor. The capsule is lodged between two layers of hyaloidea, which as they recede from each other, leave around its circumference the sacculated canal of Petit. The cornea is of horny consistency and is transparent. Light thus rapidly passes through it to the posterior part of the eye. The vitreous chamber, lying back of the crystalline lens, contains a clear jelly-like substance. THE ORGAN OF HEARING The ear, the organ of hearing, has in the fowl no conchal cartilage. The _external auditory meatus_, or canal opening, is found on each side of the head, and is usually guarded by a few stiff, short feathers. In some kinds of birds these feathers are capable of being erected so as to direct the waves of sound into the inner ear. The outer entrance of the ear contains glands. This canal is short. It leads to the drum, which is somewhat convex from the outside, and which has a membrane forming a complete curtain stretched over the outer part. The irregularly formed drum has connection with the air-containing cavity of the skull, and by a thin cartilaginous canal, the Eustachian tube, with the pharynx. The _auditory ossicles_ are represented by only a single bone, called the _columella_, which most closely represents the stapes of mammals. This is attached by processes of cartilage to the tympanic membrane. Owen considers these cartilages as representing the malleus of mammals. Huxley on the other hand considers them to represent the incus. Originating from the processes is a small muscle which is attached to the drum. This is by Shufeldt considered the Tensor tympani. The drum cavity through the fenestra vestibularis and cochlearis is connected with the labyrinth. The =inner ear= consists of a membranous labyrinth, surrounded by a spongy bony structure—the bony labyrinth. In it are recognized the vestibulum, the three half-circle shaped canals, and the cochlea. The superior semicircular canal is the largest. The acoustic nerve enters at the end of the canals near the ampullæ. The nerves are supported in delicate vascular membranes lining the canals and slightly projecting into the ampullæ. [Illustration: