GROWTH OF THE SKULL. 



231 



tlie external occipital protuberance, from which radiating lines in the bone mark the process of 

 development. The bones of the vault are exceedingly thin. Each is separate, the external 

 periosteum and the dura uniting at the edges, thus limiting the spread of an effusion under the 

 former to one bone. 



Six places where there are considerable membranous intervals between the developing 

 bones are called fontanelles. They are situated at the four angles of the parietal bones, so that 

 two are median and two are on either side. The median ones, by far the most prominent, are 

 the anterior and posterior fontanelles. The anterior fotitanelle, an important landmark in mid- 

 wifery, is a diamond-shaped space between the rounded angles of the parietals and frontals, some 

 thirty-five millimetres long by twenty-five millimetres broad. This one continues to grow after 

 birth, and is not closed till some time in the first half of the second year, or even later. The 

 posterior fo7itanelle is situated at the apex of the squamous portion of the occipital, extending 

 between the parietals. At an early stage, owing to the median fissure in the occipital, it is 

 diamond-shaped, but later it is triangular. The space is more or less filled up in the last two 

 months before birth, but it may not be truly closed for a month or two after. The anterior 

 lateral fontaneUe is a small unimportant space at the lower anterior angle of the parietal, above 

 the great wing of the sphenoid, and extending around it. It usually closes at from two to three 

 months after birth. The part between the sphenoid and squamosal is likely to persist the 

 longest. According to Sutton, ^ in early fcetal life the orbito-sphenoid bone reaches the lateral 



Fig. 261. 



Anterior lateral 

 fontanelle 



Posterior lateral fontanelle 



The skull at birth, lateral aspect. 



wall of the skull at this point, and a piece of cartilage belonging to it is found in this fontanelle. 

 It becomes bone in the course of the first year, and may unite with either sphenoid, temporal, 

 frontal, or parietal, or persist as the epipteric bone. It most often joins the parietal. The pos- 

 terior lateral fontanelle, under the corresponding angle of the parietal, extends down between 

 the temporal and the occipital. It is larger than the preceding, and may be very distinct for a 

 month or more after birth. Its complete closure is said never to occur before the twelfth month, 

 and, perhaps, usually not till the second year.^ The sagittal fontanelle (see Ossification of 

 Parietal ) may be present at the seventh month of foetal life, or later. The oblique fissure at the 

 line of junction of the two parts of the squamous portion of the occipital persists till after birth, 

 and must not be mistaken for an effect of violence. 



The mastoid process does not exist at birth. The tympanic bone is a mere frame for.the 

 ear-drum. The base of the cranium is very flat. The condyles are barely prominent, and the 

 basilar process rises but slightly. 



In the first year the outer surface of the bones of the vault becomes smooth. The bones gain 

 in thickness, and in the second year the diploe appears. At the same time the jagged points 

 develop in the sutures, and at the end of that year the metopic suture between the frontals 

 closes. 



^ Journal of Anatomy and Physiology, vol. xviii., 1884. 



^ Adachi : Ueber die Seitenfont^^nellen, Zeitschrift fiir Morph. und Anthrop., Bd. ii.. Heft 2. 



