2257. The trachea, and especially the larynx, is moreover an entire thorax, a ribbed skeleton upon a small and membranous scale. In the larynx, the animal thoracic structure, consisting of ribs and muscles, resides prognosticated. The larynx has originated from the coalescence of branchial arches. The ribs are a repetition of the branchial arches.
2258. The diaphragm is a formation, which admits, by no reasoning from its anatomy, but only genetically, of being explained. Originally, the whole body was only an abdomen, upon the external surface of which the branchiæ were appended. A remarkable instance of this is at once afforded by the Snails, and also the Fishes. As the gills were converted into lungs, a special body or the thorax originated for them, which encroached upon the abdomen. Now, the abdominal wall left between these two cavities, was just the diaphragm.
2259. The diaphragm is not a transverse wall or septum. The idea of such a cross-rail gainsays all sound physiology. It has been the abdominal wall.
2260. The union of the lungs with the nervous system is the nose.
2261. The nose is the cephalic thorax; but it has also the thoracic contents, or the very lung repeated in itself.
2262. The multicavernous ethmoid bone is the lung in the nose, the two nostrils being the stigmata or foremost openings of the trachea. The nasal muscles are homologous to the cartilages of the trachea, and especially to those of the larynx.
2263. The velum palati is the diaphragm between nose and mouth, or between the cephalic thorax and the cephalic abdomen.
Coverings.
2264. The animal coverings are desiccated respiratory organs appertaining to the integument.
Capillary Vessels.