. The comparative anatomy of the domesticated animals. Veterinary anatomy. 1046 EMBRYO LOQT. Fig. 582. A9 0 FIRST APPEARANCE OF THE LUNGS. In a Fowl at four days ; b, at six days ; c, termination of bronchus in a very young Pig- Development of the Respiratory Apparatus. Observers-are not unanimous as to the development of the lungs. According to Reichert and BischoflF, they arise from two small solid cellular masses lying on the surface of the anterior portion of the intestinal canal. These become channeled out into numerous ramifying- cavities (by the deliquescence or fusion of the internal c
. The comparative anatomy of the domesticated animals. Veterinary anatomy. 1046 EMBRYO LOQT. Fig. 582. A9 0 FIRST APPEARANCE OF THE LUNGS. In a Fowl at four days ; b, at six days ; c, termination of bronchus in a very young Pig- Development of the Respiratory Apparatus. Observers-are not unanimous as to the development of the lungs. According to Reichert and BischoflF, they arise from two small solid cellular masses lying on the surface of the anterior portion of the intestinal canal. These become channeled out into numerous ramifying- cavities (by the deliquescence or fusion of the internal cells), which communicate with the trachea. Costa states that they commence by a median, bud-like, hollow process that opens into the oesophagus. The walls of the communicating aperture elongate considerably, and at a later period form the trachea and larynx ; while the hollow bud divides into two pyriform sacs, each of which becomes broken up into a multitude of subdivisions to constitute the pulmonary lobes, with their vesicles and infundibula. The trachea is completed by the development of the cartilaginous rings in the tube that binds the lungs to the oesophagus. They appear at the commencement of the third month. The larynx is developed in the ^''g- 583. same manner at the pharyngeal open- ing. It is always somewhat unde- fined during youth, and its definitive I* volume is not acquired until the period of puberty. The thymus gJand appears as a process of the respiratory mucous membrane. It seems to be formed at the larynx, and gradually descends along the trachea to the entrance of the thorax. Development of the Digestive Apparatus. In this paragraph, the develop- ment of the alimentary canal will be first studied, then that of the organs annexed to it. A. Alimentary Canal.—We have seen how the embryo, in be- coming incurvated, divides the blasto- dermic vesicle into two parts which communicate by a large pedicle. The external portion is the umbilical. EMBRYO OF DOG, rWEN
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