Both mandibles are concave within; the palate flat, with two longitudinal ridges; the posterior aperture of the nares linear and 9 twelfths long, the anterior or external aperture entirely obliterated. The lower mandible has a distinct oblique joint at about a third of its length, enabling it to be expanded to the extent of an inch and a half. The pouch, which is small, is constructed in the same manner as that of the Pelicans and Cormorants; its muscular fibres running from the lower edge of the mandible downwards and backwards, and a slender muscle passing from the anterior part of the hyoid bone to the junction of the crura of the mandible. The tongue is reduced to a mere oblong knob, 1 1/2 twelfth long, and 1/2 twelfth in height. The aperture of the glottis is 3 twelfths long, with two roundish thin edged flaps behind, destitute of papillæ. There is a small bone appended to the occipital ridge, 1/4 inch in length, as in the Cormorants.
The œsophagus a b, is 17 inches long, exceedingly delicate and dilatable, with external longitudinal fibres, the transverse fibres becoming stronger towards the lower parts. Its diameter when moderately dilated is 1 3/4 inch at the top, 1 inch farther down, at its entrance into the thorax, 9 twelfths, and finally 1 1/2 inch; but it may be dilated to a much greater extent. The proventricular glands, instead of forming a belt at the lower part of the œsophagus, are placed on the right side in the form of a globular sac, about an inch in diameter, communicating with the œsophagus, b, and stomach, d. For two inches of the lower part of the œsophagus, b, or at that part usually occupied by the proventriculus, the transverse muscular fibres are enlarged, and form an abrupt margin beneath; on the inner surface there are four irregular series of large apertures of gastric glandules or crypts. The proventriculus itself, c, is composed of large crypts of irregular form, with very wide apertures, and covered externally with muscular fibres. The stomach, d d, is roundish, about an inch and three quarters in diameter, with two roundish tendinous spaces, e, and fasciculi of muscular fibres; its inner coat thin, soft, and smooth. It opens by an aperture a quarter of an inch in diameter into a small sac, f, precisely similar to that of the Pelican, which has a muscular coat, with a soft even internal membrane, like that of the stomach. The pylorus has a diameter of 2 twelfths, is closed by a semilunar valve or flap, and is surrounded by a disk of radiating rugæ three-fourths of an inch in diameter. The intestine, g h, is 3 feet 4 inches long, its average diameter 2 1/4 twelfths, but only 1 twelfth at its junction with the rectum, which is 3 1/2 inches long, 3 twelfths in diameter. The cloaca globular, 1 1/2 inch in diameter. There are no cœca properly so called, but a small rounded termination of the rectum 2 twelfths in length as in the Herons.
The subcutaneous cellular tissue is largely developed, and the longitudinal cells on the neck are extremely large, as in Gannets and Herons. The olfactory nerve is of moderate size, and the nasal cavity is a simple compressed sac 4 twelfths in its greatest diameter. The external nares are closed, and there are no supraorbital glands. The external aperture at the ear is circular, and not more than half a twelfth in diameter.
The trachea is 13 1/2 inches long, much flattened, narrow at the upper extremity, where it is 2 1/2 twelfths in breadth, enlarging gradually to 4 1/2 twelfths, and toward the lower larynx contracting to 2 1/2 twelfths. The rings are very slender, unossified, and feeble; their number 230; the bronchial half-rings 25. The contractor muscles moderate; sterno-tracheales; and a pair of inferior muscles going to the last ring.
In a young bird scarcely two days old, and measuring only 3 3/4 inches in length, the two most remarkable circumstances observed refer to the nostrils and stomach. The posterior or palatal aperture of the nares is of the same form, and proportional size, as in the adult; the nasal cavity is similar; but there is an external nasal aperture, or nostril, on each side, so small as merely to admit the mystachial bristle of a Common Squirrel. The stomach is of enormous size, occupying three-fourths of the cavity of the thorax and abdomen, being 10 twelfths of an inch long, and of an oval shape. The proventriculus is separated from the stomach and formed into a roundish lobe, as in the old bird; and beside it is the lobe or pouch appended to the stomach, and from which the duodenum comes off. Even at this very early age, the stomach was turgid with a pultaceous mass apparently composed of macerated fish, without any bones or other hard substances intermixed.
Here then we have an instance of external nares in the young of a bird in which they are entirely obliterated in the adult.
SURF DUCK.
Fuligula perspicillata, Bonap.
PLATE CCCXVII. Male and Female.