Part 53

=The Tongue= (Fig. 27, No. 3). Location.—The tongue (lingua) of the fowl is situated in the floor of the mouth between the rami of the lower mandible, and is slung to the cranium by the cerato-branchial element of the os hyoideum (Fig. 18, No. 2).

Shape.—The tongue, is pointed in front and wide behind, shaped like an Indian arrow-head, and is supported by the bony and cartilaginous hyoid apparatus (Fig. 9, A).

FIG. 31.—The visceral organs of the hen. 1, Tongue. 2, Larynx. 3, Glottis. 4, First portion of the esophagus. 5, Crop. 6, Second portion of the esophagus. 7, Proventriculus. 8, Duodenum. 9, Free or floating portion of the small intestine. 10, Mesentery supporting the free portion of the small intestine. 11, Cæca. 12, Rectum or large intestine. 13, Cloaca. 14, Anus. 15, Liver. 16, Gall-bladder. 17, Pancreas. 18, Gizzard. 19, Trachea. 20, Lungs. 21, Spleen. ]

Structure.—The free part of the tongue consists of two long tubes which are formed by the rolling in of the ventral sides of its horny coverings. The dorsal plate, which constitutes one-half of the horny sheath, does not form a part of the tubes, but ends in the region of the point of the entoglossum.

The top surface is covered by a thick stratum corneum, giving it a rather horny surface. Glands occur in the posterior part of the tongue.

While not so freely movable as in mammals, the tongues of birds are very flexible.

=The Pharynx= (Fig. 27). Location.—The anterior part of the pharynx joins with the mouth and the posterior part with the upper portion of the esophagus and the superior larynx. The pharynx is bounded anteriorly by the base of the tongue and by the posterior edge of the hard palate. Posteriorly, it is marked by the entrance of the esophagus and by a ridge of filiform papillæ located on the supero-posterior part of the larynx, called the palatal papillaries. A few filiform papillæ stud the roof. The pharynx communicates anteriorly with the posterior nares and the mouth, and, posteriorly, with the esophagus and the larynx.

Shape.—The pharynx is a musculo-membranous sac.

Structure.—The pharynx is lined with a mucous membrane covered by squamous epithelium. The mucous membrane is thrown into irregular folds. The bird has two Eustachian tubes. Pneumatic apertures conduct the air from the Eustachian tubes to the pericranial diploë.

In the posterior pharyngeal roof is situated the infundibular crevice.

Function.—The function of the pharynx is to give passage for the air from the posterior nares to the larynx, and to give passage for the food from the mouth to the esophagus.

=Glands Adjacent to the Mouth and to the Pharynx.=—The mucous membrane adjacent to the glottis and in the roof of the mouth contains alveolar glands. The angular gland of the mouth, located beneath the zygomatic arch, by some anatomists is considered the rudimentary parotid gland. The sublingual glands, or glandulæ sublinguales, are well developed (Fig. 17, No. B, 4). They form conical masses, with the apex directed anteriorly, and occupy a portion of the intermaxillary space. Several ducts from these glands open into the mouth cavity. In the palatine region there are also located glands called the palatine glands, which open by many stomata upon the surface.

=The Esophagus= (Fig. 18, No. 6). Location and Shape.—The esophagus is a musculo-membranous tube, capable of great distension, which extends from the pharynx to the proventriculus (Fig. 35, No. 1, and 3).

The esophagus communicates anteriorly with the pharynx. It extends down the neck, lying supero-laterally with regard to the trachea and toward the right side. It enters the thorax above the trachea, and, passing through between the bronchi, terminates into the proventriculus. At the entrance of the thorax and just to the right of the median line, it expands into the crop which divides it into two portions, designated as the first and the second. The first portion of the esophagus is the longer, the length depending upon the size and kind of fowl.

Structure.—The wall is composed of four coats, the mucous membrane, the submucosa, the muscular coats, and the fibrous sheath or tunic. The mucous membrane is pale and is covered with stratified squamous epithelium.

The mucous membrane is loosely attached to the muscular coat by the submucosa. Except during deglutition it lies in longitudinal folds which obliterate the lumen. Opening from the mucosa are lenticular glands, which may be seen on inflating an esophagus and looking through its transparent walls.

The muscular coat of the esophagus is divided into two layers, an outer longitudinal and an inner circular layer.

The outer fibrous sheath connects the esophagus loosely to the surrounding structures.

Function.—The function of the esophagus is to give passage way for the food from the pharynx to the crop and from the crop to the proventriculus.

=The Crop= (Fig. 35, No. 2; Figs. 30 and 31). Location and Shape.—The crop, or ingluvies, saccular in shape, is located at the entrance of the thorax and just to the right of the median line. The first portion of the esophagus empties into the crop superiorly and inferiorly the crop opens into the second portion of the esophagus. Like the esophagus the crop is capable of great distension.

Structure.—The wall of the crop is composed of four coats, the mucous membrane, submucosa, muscular and the outer fibrous.

The crop is lined with mucous membrane containing mucous glands which secrete a mucus to keep the surface moist. The surface of the mucous membrane is covered by stratified squamous epithelium.

The submucosa connects the mucous membrane to the muscular coat.

The wall of the crop is provided with strong muscles. The fibrous coat, or tunic, connects it with the surrounding structures.

Function.—The crop is a storehouse for the food during the hours of feeding, the food when needed by the stomach being gradually discharged from the crop by the contraction of its muscular walls. The subcutaneous cervical muscles which cover this reservoir aid in this discharge.

In the act of deglutition, the food, after being subjected to the fluid supplied in the mouth by the adjacent glands, is poised upon the tongue and swallowed partly by a sudden jerk of the head, and partly by means of the pressure of the tongue against the hard palate, the food then passes down the esophagus and lodges first in the crop, till needed by the stomach, when it is passed through the second portion of the esophagus to the first portion of the stomach, the proventriculus. The time during which food remains in the crop depends upon the nature of the food. Animal food will, in part, be retained about eight hours and vegetable foods may not all be passed on for from sixteen to eighteen hours.

=The Stomach= (Fig. 31, No. 7; Fig. 32, B).—The stomach, or ventriculus, of fowls is made up of two portions, namely, the pars glandularis, or proventriculus, and the pars muscularis, or gizzard.

=The Proventriculus.= Location.—The proventriculus lies in the superior part of the groove formed by the two lobes of the liver, is inferior to the aorta, and is directed slightly to the left, communicating anteriorly with the second portion of the esophagus and posteriorly emptying into the pars muscularis, the gizzard.