It is probable that the cortical portion is derived from the ingrowths of the peritoneum, and the medullary cords from the sympathetic ganglion. The cells are cylindrical or polygonal in shape, with an eccentric substance between the columns. The cords, or columns, form between them, elongated channels which extend into the interior of the gland and end as blind or cæcal extremities. Large ganglionic nerve cells belonging to the sympathetic system occur near the surface of the gland. The blood-vessels are not well developed in the interior of the gland but are numerous and of good size in the outer parts. Lymph vessels are also present. _Function._—The adrenals are ductless glands. They secrete an internal secretion, or hormone, which influences the tonus of the blood-vessels. An extract from these glands is called adrenalin. THE RESPIRATORY APPARATUS (Figs. 50 and 61, _A_) Owen says: “Notwithstanding the extent and activities of the respiratory function in birds, the organs subservient thereto manifest more of a reptilian than of the mammalian type of formation.” By the action of the respiratory organs certain chemical and physical changes take place in the blood. The chief of these consists in absorption of oxygen from, and giving off carbon dioxide to, the atmospheric air, the former changes being necessary for the elaboration of the fluid, the latter for the elimination of a substance which, if retained, would prove injurious. The organs of respiration are invariably adapted to the wants of the animal and the medium in which it lives. In the bird, which breathes through its nose, the organs of respiration are nostrils, nasal chambers, pharynx, superior larynx, trachea, inferior larynx, bronchi, bronchial tubes, lungs, and air-sacs. =The Nostrils and the Nasal Chambers.=—The nostrils of the bird open externally by two small elliptical openings, which pierce the upper mandible. Within each nasal chamber (Fig. 26, _A_) are three turbinated laminæ, or _turbinated bones_. The inferior one is a simple fold adhering to the lower and anterior part of the nasal septum. The middle turbinated bone is the largest. It is of infundibular form, and adheres by its base to the septum and externally to the side wall of the nose. It is convoluted with two and a half turns. The superior bone, of bell shape, adheres superiorly to the frontal bone. The internal turbinated bone extends toward the orbit; the external terminates in a cul-de-sac behind the middle turbinal (Fig. 26, No. _A_, 1 and 2, and _G_). The nostrils are separated by a partition which is partly bony and partly cartilaginous. The posterior nares is represented by a long slit in the hard palate. =The Pharynx and the Superior Larynx.=—A transverse row of horny, filiform papillæ marks the anterior border of the pharynx, where in other animals the soft palate, or velum, is located. (For further description of the pharynx see special chapter.)