Fig 303.—Head of Woodpecker.
c, tongue; a, b, d, hyoid bone; e, q, windpipe; f, salivary gland.
Do you see any signs of teeth in the bird’s jaws? Why are duck’s “teeth” (so called by children) not teeth? Can the tongue of a bird be pulled forward? (Fig. [303].) What is its shape? If there is opportunity, dissect and study the slender, bony (hyoid) apparatus to which the base of the tongue is attached (Fig. [303]), the opening of the windpipe, or trachea, the slitlike opening of windpipe, which is so narrow as to prevent food falling into the windpipe.
Fig. 304.—Anatomy of Dove × ½.
bk, keel of breastbone; G, g, brain; lr, windpipe; lu, lung; h, heart; sr, gullet; k, crop; dr, glandular stomach; mm, gizzard; d, intestine; n, kidney; hl, ureter; eil, openings of ureter and egg duct into cloaca, kl.
Fig. 305.—Food Tube of Bird.
P, pancreas; C, cæca.
Question: Identify each part by means of Fig. [304].
The Internal Organs, or Viscera (Figs. [304] and [305]).—The viscera (vis’se-ra), as in most vertebrates, include the food tube and its glands; the lungs, the heart, and the larger blood vessels; the kidneys and bladder and the reproductive organs. The lower part, or gullet, is enlarged into a crop. It is largest in grain-eating birds. It is found in the V-shaped depression at the angle of the wishbone, just before the food tube enters the thorax. The food is stored and softened in the crop. From the crop the food passes at intervals into the glandular stomach. Close to this is the muscular stomach, or gizzard. Are the places of entrance and exit on opposite sides of the gizzard, or near together? (Fig. [304].) Is the lining of the gizzard rough or smooth? Why? Is the gizzard tough or weak? Why are small stones in the gizzard? Why do not hawks and other birds of prey need a muscular gizzard? The liver and pancreas empty their secretions into the intestines by several ducts a little way beyond the gizzard. Beyond the mouths of two cæca (Fig. [305]) the many-coiled intestine empties into the straight rectum, which terminates in a widened part called the cloaca. Not only the intestine, but the two ureters of the urinary system and the two genital ducts of the reproductive system all empty into the cloaca (Figs. [304], [305]).
Fig. 306.—Position of Lungs and Air Sacs (Pigeon).
Tr, windpipe; P, lungs; Lm, sac under clavicle with prolongation (Lh) into humerus; La, sacs in abdomen.
The lungs have their rear surfaces attached to the spinal column and ribs (lu, Fig. [304]). They are connected with thin-walled, transparent air sacs which aid in purifying the blood. When inflated with warm air, they probably make the body of the bird more buoyant. For the names, location, and shape of several pairs of air sacs, see Fig. [306]. The connection of the air sacs with hollows in the humerus bones is also shown in the figure. Many of the bones are hollow; this adds to the buoyancy of the bird. The pulmonary artery, as in man, takes dark blood to the lungs to exchange its carbon dioxide for oxygen. Of two animals of the same weight, which expends more energy, the one that flies, or the one that runs the same distance? Does a bird require more oxygen or less, in proportion to its weight, than an animal that lives on the ground? Are the vocal chords of a bird higher or lower in the windpipe than those of a man? (Fig. [307].)