Should any one, in practice, forgetting this doctrine, bring the forehead to the pubis, he would do a great wrong; for, as the chin must be born first, and the occiput last, the chin will have to slide along the whole length of the sacrum five inches; and over the extended perineum two and a half or three inches before it can escape; but, to do this, it will be required that the head and half the thorax of the child shall be together jammed within the excavation; for from the chin of the child to the top of its sternum are not eight inches. Such a position is almost sure to demand an embryotomy operation for the delivery of the foetus.

CHAPTER III.

OF THE CHILD'S HEAD AND OTHER PRESENTING PARTS.

THE study of the form and dimensions of the child derives its importance from the relations of the foetus to the bony pelvis, through which it is destined to pass in the act of parturition.

To know the form and magnitude of the head, as related to the pelvic canal, is of the highest importance; and, indeed, no man should be looked upon as a qualified practitioner who suffers himself to remain ignorant of every particular of the matter now referred to.

The foetal cranium, divested of the bones of the face, closely resembles in form an ostrich egg, upon the side of the lesser pole of which the facial bones are adjusted.

In the figure of the foetal head which is annexed (Fig. 28), it is evident that if the bones of the face were removed, the remainder of the cranium would be oviform; as I have on different occasions shown it to be, by removing those bones in presence of my class at the Medical College.

a

Fig. 28.

In looking at the head from above downwards, as in Fig. 29, the bones of the face are out of sight, and the cranium is evidently egg-shaped, the greater pole being at the occiput, while the lesser is at the forehead.

The foetal head (Fig. 30) is copied with the camera from a cast of a foetal head, and gives a proper idea of the true form when covered with its integuments: the child perished in the labor, its head being too large to pass through the straits without the aid of the forceps.

The longitudinal diameter of this oviform skull has, by most authors, been computed at four inches, and its conjugate at three inches and a half; both of which calculations are considerably under the mark of truth, as I have found by careful measurement.

The bones that enter into the composition of the skull, excepting

the face pieces, are the os occipitis, the two ossa parietalia, the os frontis, the two ossa temporum, and the sphenoides. These are the bones that make up the principal bulk of the object, for the face bones do not add very considerably to the magnitude of the mass.

The face bones are the maxilla inferior, the maxilla superior, the ossa malarum, ossa nasi, ossa palati, and the vomer. It seems hardly necessary to mention the ethmoides and the ossa unguis.

In a new-born child, the process of ossification is not completed, and the edges of the cranial bones are not locked or dovetailed together by the serræ of the adult suture; whence it happens that the cranium is not a fixed magnitude or form, but liable to alteration under the pressure of the parts through which it is driven by the great force of the labor-pains.

A great advantage is found in this mobility of the cranial bones, in certain instances in which the pelvic circumference is too small, either absolutely or relatively; for, the child's head of four inches in its conjugate diameter may, by the pressure, become reduced or wire-drawn so as to pass through a superior strait of only three and a half inches, or even less; and that without injury to the head, which, as soon as it has escaped from the pressure, begins to recover its normal form again.

There are, however, to be met with many specimens of the foetal cranium so solid and firm in their ossification as to yield not at all in labor, which is then rendered both more painful and difficult. The young practitioner therefore should, in difficult cases, take comfort from discovering by the touch that the foetal head is of a yielding nature, and hence not likely to resist too long the moulding or modelling efforts of the throes.

Size of the Foetal Head.-In the foetal head at term, of which there is a drawing at Fig. 30, we are in the habit of imagining certain lines called diameters, which are represented in Fig. 28. There is a line traced from the chin a, to the vertex or point of the head or occiput b, called by the English writers the oblique diameter, but which the French authors have induced us, of late, to denominate occipito-mental diameter, a phrase that explains itself. The next one is the line from d to e, called the occipito-frontal diameter, as indicating the distance from the occiput to the most salient point of the forehead. After this comes the perpendicular diameter, from c to h; and lastly, in Fig. 29, the transverse or bi-parietal diameter, which passes from one parietal protuberance to the other, from a to b; and the temporal diameter, from c to d.

As to these diameters, I have never deemed it expedient that the Student should charge his memory with all of them; yet he ought to know that the occipito-mental diameter is above five inches in length. He ought to know this, in order that he may also know that such a diameter cannot be see-sawed, or reversed, after the head has once fairly entered into the excavation, in which no space exists large enough to render such a change possible. If the extremity b descends first, it must escape first, or be returned above the superior strait; and if the extremity a descend first, it must escape from the inferior strait first, or be returned above the linea ileo-pectinea, in order to be there see-sawed.

The occipito-frontal diameter e a is four inches and ten-twelfths of an inch in length-a diameter too considerable to admit of its being see-sawed in the excavation, except under very extraordinary circumstances, for there is, in general, not space sufficient for that end.

I speak with very great confidence as to the above estimate, for I have carefully measured and recorded the size of three hundred crania of mature children that I received in the course of my obstetric practice. The Student will be in error if he adopts the common estimate of the authorities, which is too low at four inches.

In a single series of one hundred and fifty heads, I found the occipito-frontal diameter in fifty-two of them to exceed 5 inches. In 11, it was 5th; in 8, 5,2ths; in 3, it was 5,3ths; in 1, 5,4ths; in 1, 5ths; in 2, 5,7ths; and in 1, 510ths.

The sum of my occipito-frontal measurements was seven hundred. and twenty-nine inches and seven-twelfths of an inch for one hundred and fifty crania. The mean was four inches ten-twelfths. The sum of the bi-parietal diameters of the said one hundred and fifty crania

was five hundred and eighty-six inches and seven-twelfths-the mean, three inches and eleven-twelfths of an inch.

The bi-parietal diameters exceeded four inches in sixty-eight of the children. In 19 it was 4.1; in 5 it was 4.2; in 6, 4.3; in 3, 4.4; in 1, 4.5; in only one case was it less than 3.6, the usual estimate, and in that case it fell to 3.4.

A paper containing statements of the above series was read by me at the centennial celebration of the Amer. Phil. Society, on the 25th May, 1843, and was published in the Proceedings, &c., vol. iii. p. 127.

I measured one hundred and twenty-six occipito-mental diameters of neonati at term, of which the sum was six hundred and ninety-nine inches and five-tenths, so that the mean or average of the one hundred and twenty-six diameters was five inches and a half. I know no one who has measured so many, and I am sure that greater accuracy is not to be attained by any person.

Upon these grounds, therefore, I am to inform the Student that the occipito-mental diameter of the foetus is five inches and a half, the occipito-frontal four inches ten-twelfths, and the bi-parietal three

inches eleven-twelfths.

The above statements ought to show that it is not a matter of small moment whether the head presents in labor by the vertex, the crown, or the forehead.

Upon the presentation depends the circumference of the advancing body; if the vertex presents, we have a circumference equal to thrice the bi-parietal diameter, which would equal a circle of eleven inches and three-quarters in circumference. The occipito-frontal diameter would give a circumference of upwards of fourteen inches, while the occipito-mental circumference would not be much under sixteen inches.

Fontanels.-The bones of the head are divided from each other by the sutures. In Fig. 29, showing a top view of the skull, may be seen the sagittal suture, a straight line which extends from the middle, and sometimes from the base, of the os frontis backwards, to the upper angle of the occipital bone, where it appears to divide, branching into the two legs of the lambdoidal suture. In passing from the forehead backwards, this sagittal or arrow suture crosses the transverse or coronal suture, and at the place of crossing there is a large vacuity, as to bone, which is occupied, however, by the skin and by strong membranes which constitute what is commonly called the mould of the head-technically, the anterior fontanel, the great fontanel, the