68 



BOXES OF THE HEAD. 



condylar and tabular pai-ts, beginning- in the second or thii-d. is completed in 

 the fourth year ; that of the basilar and condylar parts, beginning in the thii-d or 

 fourth, is completed in the fifth or sixth year. The basi-occipital is united to 



.^V!^p^rrs.^ 



Fig. 56. V> Fig. 56.— Ossification of the 



Occipital Bone (R. Quain). 



A, in a foetus of 10 weeks 

 (from Meckel, Archiv, vol. i. 

 tal>. vi.) ; a, upper or tabular 

 2)ai't ; 1 & 2, lower and upper 

 pail's of ossific centres in it ; 

 b, lower part or basilar and 

 condylar portions : ossific cen- 

 tres ai-e seen in tlie condylar 

 liortions. 



B, occipital bone of a child 

 at birth ; a, upper or tabular 

 part, in ■which the four centres 

 have become iinited into one, 

 leaving fissures between them ; 



c b, b, the ossified condylar por- 



tions ; c, the basilar portion. 



the basi-sphenoid by intervening cartilage up to the twentieth year, after which 

 ossific union begins and is completed in one or two years. 



Tlie parietal bone is ossified from a single nucleus, which aj^pears in the 

 parietal eminence about the seventh or eighth week. The embience is very 

 conspicuous in the young bone, and gives a marked character to the fonn of 

 the skull for a number of years in early life. 



The frontal bone is ossified from two nuclei which appear one on each side 

 above the orbital arch, about the seventh week. At bii-th the bone consists of 



Fig. 57. 



Fig. 57. — Frontal Bone of a Fietus shoktlt 

 BEFORE Birth (R. Quain). 



a Scb indicate the two separate portions of 

 tlie bone, in each of wliich tlie radiation of 

 bony spicula from the frontal eminence is 

 seen. 



two separate lateral portions, which unite 

 by a vertical median sutui'e duriug the 

 first year. This frontnl SKfiD-e usually 

 becomes obliterated by osseous union 

 taking place from below upwards, during 

 the second year, though not unf requently 

 The frontal sinuses appear dming the fii'st year, and 

 go on increasing in size up to old age. 



The Fontanelles. These are membranous intervals between the incomplete 

 angles of the parietal and neighboui'ing bones, in some of which movements of 

 the soft wall of the cranium may be observed in connection with variations in 

 the state of the circulation and respiration. They are four in number, two 

 median, anterior and posterior, and two lateral. Tlie a ?)tcrior fontanelle. situated 

 between the anterior superior angle of the parietal bones and the superior angles 

 of the ununited halves of the frontal bone, is quach-angular in form, and remains 

 open for some time after birth. The jxixfcrior fontanelle, situated between the 

 posterior superior angles of the parietal bones and the superior angle of the 

 occipital bone, is triangular in shape. It is filled up before bu-th, but the edges 

 of the bones, being united by membrane only, ai-e still freely movable upon each 

 other. The lateral fontanelles, small and of iiTegular form, are situated opposite 



it persists throughout life. 



