The changes from the foetal state take place from the moment the child breathes; but the cause of its breathing has puzzled the ablest physiologists. The necessity of taking breath has been attributed to irritation, to an"appetite for air," and to innumerable fancied causes. The real cause appears to be change of position. The foetus, in the womb, assumes that position, which the superior strength of the flexor muscles produces. The body is bent forward, the knees drawn up, the legs backward, the arms across the body, and the fingers clenched. When the position is altered the ribs are raised, and the abdominal viscera fall down. A vacuum is the consequence in the lungs, which the air rushes in to supply. The sensation of uneasiness induces the necessity of expelling the air; and the same

4R 2 causes concur to bring on the repetition of breathing, which, from the uneasy feeling excited by the necessity for inspiration and expiration, is regularly continued.

In consequence of the expansion of the lungs, a larger portion of blood is carried into that organ; the right ventricle is more completely emptied, and the impetus which kept the foramen ovale open, and which carried the blood through the ductus arteriosus, is lessened; they gradually contract into ligaments, and the whole of the fluid, brought by the veins, is carried through the lungs. When the supply from the umbilical cord is cut off, the ductus venosus contracts in the same way, and the vena portae receives the blood from the returning veins of the abdominal viscera, as in the whole extent of the future life.

The foetus differs, in many respects, from the adult, even after the changes enumerated have taken place. The head is very large in proportion to the rest of the body, the bones of the head soft and yielding, the sutures not yet formed, and a triangular space is left at the union of the coronal and sagittal sutures. The bones of the trunk, the extremities, and all the articulations, are remarkably flexile. All the protuberances of bones (apophyses) are distinct osseous portions, united by cartilages (epiphyses); the heads and condyles of bone, as well as the brims of cavities, are cartilaginous.

The brain and spinal marrow, the glandular and sanguiferous systems, are, we have said, larger than in the,adult. A gland, peculiar to the foetus and infant, is found at the upper part of the mediastinum, between its folds, which disappears in advanced age, and is apparently connected with the lymphatic system. The kidney is also divided into distinct lobes, as in brutes.

In the foetus, the cavity of the thorax is, as may be expected, less than after respiration; the lungs are smaller, more compact, and of a red colour like the liver. The abdomen is disproportionately large, and 'he extremities particularly small.

It has been supposed, that if a child, who has only once or twice breathed, be thrown into water, the foramen ovale may continue open, and he may enjoy the advantages of living in air or under water. This idea is supported by the remark, that negroes are excellent divers, and that they are usually plunged into water as soon as they are born. The supposition is not impossible, but has never been reduced to practice. We have a faint recollection of the experiment having been tried on puppies without success.

The extra-uterine foetuses are lodged either in the ovarium, in the Fallopian tubes, or in the cavity of the abdomen. One instance is recorded where the foetus was found in the cavity of the abdomen, the uterus, Fallopian tubes, and ovaria, being at the same time in an unaltered state, similar to what happens where impregnation has not taken place. This and other appearances will, however, be readily understood, when we speak more particularly on the subject of Generation, q. v. (See Medical Memoirs, London, vol. iii. p. 176.) When extra-uterine foetuses die, the weight, after some time, occasions an irritation, and an abscess is formed, by which the child generally comes away by parts. See instances recorded in the London Medical Observations and Inquiries, vol. ii. and iii. See also Dr. Hamilton's Outlines of Midwifery; Ilallcr's Physiology;

Sabatier's Description of the Foetus; Wrisberg's Ob-servationes Anatomicae; and Dr. Hunter's Tables.