OSSIFICATION OF CRANIAL BONES. 



67 



die Visceralbogen," Muller's Archiv, 1837. See for a figure of Meckel's cartilage the 

 description of the bssicles of the ear, under the Organs of the Senses.) 



OSSIFICATION. The occipital bone, for some time after birth, consists of four sepa- 

 rate pieces, a basilar, a tabular, and two condyloid parts. The lines of junction of the 



Fig. 59. OSSIFICATION OP THE 

 OCCIPITAL BONE. 



A, in a foetus of 10 weeks 

 (from Meckel, Archiv, vol. i. 

 tab. vi.); a, upper or tabular 

 part ; 1 & 2, lower and upper 

 pairs of ossific centres in it ; 

 b, lower part or basilar and 

 condyloid portions : ossific cen- 

 tres are seen in the coudyloid 

 portions. 



B, occipital bone of a child 

 at birth; a, upper or tabular 

 part, in which the four centres 

 have become united into one, 

 leaving fissures between them ; 

 6, 6, the ossified condyloid por- 

 tions ; c, the basilar portion. 



Fig. 59. 



basilar and condyloid parts pass through the condyles near their anterior extremities ; 

 those of the condyloid and tabular parts extend outwards from the posterior extremity 

 of the foramen magnum. The basilar. and condyloid parts arise each from one osseous 

 nucleus. In the tabular part there are probably in most cases four nuclei, placed in 

 pairs above and below the occipital protuberance : Meckel mentions four additional 

 nuclei, placed two at the superior and one at each lateral angle (" Handbuch der 

 Mensch. Anat.," ii. 543) ; the different nuclei speedily unite to form a single thin 

 tabular mass. 



The parietal bones are ossified each from one nucleus which is placed near the 

 centre of the bone or at the parietal eminence. 



The frontal bone consists for a year, or from one to two years after birth, of two 

 lateral portions, which not unfrequently remain separate during life (as happens also 



Fig. 60. 



Fig. 60. FRONTAL BONE OP A FCKTUS SHORTLY 

 BEFORE BIRTH. 



a & 6 indicate the two separate portions 

 of the bone, in each of which the radiation 

 of bony spicula from the frontal eminence 

 is seen. 



in the majority of animals), with a vertical 

 suture between them, the frontal suture. 

 Ossification begins on each side from a 

 single nucleus above the orbit, or in the 

 place of the frontal eminence. 



The Fontanelles. Opposites the angles of 

 the parietal bones, there are spaces which 



remain unoccupied by bone, after the osseous wall of the skull is elsewhere completed. 

 Two of these, the anterior and posterior fontanelles, are in the middle line ; the 

 lateral fontanelles, two on each side, are opposite the inferior angles of the parietal 

 bones, and are less important. The anterior fontanelle, situated between the adjacent 

 angles of the parietal bones and the ununited halves of the frontal bone, is quadran- 

 gular in form, and remains open for some time after birth. The posterior fontanelle, 

 situated between the parietal bones and the superior angle of the occipital bone, is 

 triangular ; it is filled up before birth, but during parturition the compression of the 

 child's head forces the angle of the occipital bone beneath the edges of the parietals, 



F 2 



