FCETAL HEAD. 179 



yield in either of its diameters to the expulsive powers of the ute- 

 rus. The latter provision, however inconvenient in parturition, 

 is of the greatest consequence immediately afterwards; for with- 

 out this immobility in the base of the cranium, whenever the 

 weight of the head was thrown upon it, the pressure of the ver- 

 tebral column would drive it upwards, to the injury of the brain 

 and of the nerves proceeding from it. This resistance, it may 

 be added, is still farther assisted by the arched figure of the base 

 of the cranium. On this subject, it is not a little remarkable, 

 that even the heads of hydrocephalic foetuses have the bones 

 of the base fully ossified, and in contact, so as to support the 

 weight of the head in the vertical position. 



Fontanels. In consequence of the flat bones of the cranium 

 ossifying always towards the circumference, their angles, as ob- 

 served, being the longest radii from their centres, are the last in 

 ossifying. These angles are commonly incomplete at birth, and 

 the membranous spaces which represent them are the Fontanels. 

 Of these there are six, two on the middle line of the head, above, 

 and two on either side. The former afford highly important 

 indications to the midwife. 



The anterior fontanel is the largest of all. It is at the fore 

 part of the sagittal suture, and is produced by a deficiency in 

 the angles of the parietal bones, and of the contiguous angles of 

 the os frontis. It is quadrangular or lozenge-shaped; and the 

 anterior angle is generally longer than the others. This is re- 

 markably the case, when the sagittal suture is continued down 

 to the root of the nose. The posterior fontanel is at the other 

 extremity of the sagittal suture, and as there are only three 

 points of bone defective there, two for the parietal bones, and 

 one for the occipital, this suture is triangular. In many chil- 

 dren, at birth, it is so far filled up as to be scarcely visible; the 

 three membranous sutures, however, which run into it, make 

 its position sufficiently discernible by the finger. 



Of the two fontanels, on either side, one is placed at the an- 

 gle of the temporal bone where it runs up between the occipital 

 and the parietal. The other is in the temporal fossa, under the 

 temporal muscle, at the junction between the parietal and the 

 sphenoidal bones. These two fontanels are but little referred 

 to by the accoucheur in delivery, as they are irregular and in- 

 distinct. The pulsations of the brain may be readily felt through 



