Elements of Physiophilosophy

by Lorenz Oken

2773. In the act of respiration two orders of muscles are active, the proper-pectoral muscles, and the abdominal muscle, which has been displaced from the thorax, or the diaphragm.

2774. As originally the thorax took its rise at the expense of the abdomen, so also is every inspiration an elevation of the thorax and a displacement of the abdomen. Every breath or in-draught of air expands and produces the thorax, but narrows and arrests the abdomen. The diaphragm expresses this contest. Its contraction being a result of the respiratory tension, expresses consequently a preponderance of the thorax, and in obedience to this, narrows and diminishes the abdomen. It is supplied, in conformity with its origin, by nerves from the upper cervical vertebræ, since prior to this the abdomen extended as far as the head, and the branchiæ were appended to it as lateral strips of integument—as in Fishes.

2775. As the thoracic cavity is drawn by the diaphragm's descent towards the abdomen, so by the pectoral muscles is it raised upwards to the head. The latter movements are what is animal in the respiratory process, for they lift the thorax towards the head. Pectoral muscles and diaphragm stand opposite to each other, like limbs and trunk; the ribs are the limbs, the diaphragm the upper abdominal tunic or covering. Through this antagonism what is limbed, as belonging to the thoracic cavity, is drawn upwards, what is abdominal in its character, downwards; the result is expansion, and through this pumping in of the air.

2776. The air is in part voluntarily swallowed like the food, as e. g. by the movement of the ribs, in part involuntarily by the diaphragm. The diaphragm may be termed the heart of the abdominal cavity.

2777. In the lower organized animals, where merely branchiæ are present, the animal motion encroaches but little upon the act of respiration. In Molluscs and Snails, the oxygen is almost always on the branchiæ, as is the case also in Insects. In Fishes the water is still taken in like the food through the mouth, and driven out or expelled by the pharyngeal muscles from between the branchiæ. In them the air is in both respects swallowed. In many Reptiles the air is indeed drawn in through the nostrils, but conveyed into the lungs by a true act of deglutition. These kinds of functions are necessary, because as yet the whole trunk is abdomen, and the thoracic cavity has not as yet separated from it; hence the diaphragm is wanting.

2778. The respiratory originates therefore from the digestive organ; it is freely developed only from the abdomen, and is at length entirely liberated from the latter as a self-substantial cavity, e. g. first of all in the Mammalia. Respiration is originally but an act of deglutition, which has gradually become perfected, by the animal trunk being associated with it to a greater extent.

2779. The pumping in of air has therefore become in the highest degree a process of suction, and in this resembles the digestive function when it has become animal.

2780. Then also the air passes no longer through the mouth, but through the nose, as being the peculiar opening of the thoracic cavity in the head. Even the Fishes have as yet no nostrils opening into the mouth.

2781. The thoracic motion is a limb-motion, and would become locomotion, were the ribs not conjoined. In many of the lower animals the branchiæ are at once organs of motion, such as fins or rudders.

2782. Every inspiration is a self-manning towards the animal; every expiration a retro-depression unto the plant; the abdomen in this case regains the upper hand from the diaphragm reverting to its usual position, and the thoracic cavity narrowing. Respiration is a becoming animal.