62 



A MANUAL OF ANATOMY 



on either side of the middle hne not far from the future superior angle, which 

 occasionally remain as separate ossicles, or they may fuse and give rise to 

 the pre-interparietals. The interparietal portion may remain separate from 

 the supra-occipital, with which it may be connected by a suture, or they may 

 be separated by a partial fissure. Fissures, which persist for some time after 

 birth, intersect the tabular part at the superior and lateral angles, and a 

 membranous interval extends from the protuberance to the foramen magnum 

 in early life, which remains for some weeks, after which it is replaced by bone. 



It is in this latter situ- 

 ation where an ence- 

 phalocele may occur. 

 The basilar and con- 

 dylar parts have each 

 one centre appearing 

 in cartilage about the 

 ninth week, the an- 

 terior part of each 

 condylar portion de- 

 riving its ossification 

 from the basilar cen- 

 tre. At birth the bone 

 is in four parts, con- 

 nected by cartilage. 

 Union between the 

 tabular and condylar 

 portions is completed 

 by the fourth year, 

 and the condylar and 

 basilar portions unite 

 about the sixth year. 

 After the twentieth year 



_ , Tabular Part. 4 Centres, which 

 appear about the 8th Week 

 (intra-uterine) 



— Obstetrical Hinge-joint of 

 Budin 



^ Condylar Part, i Centre, which 

 appears about the 9th Week 

 (intra-uterine) 

 Basilar Part, i Centre, which 

 appears about the gth Week 

 (intra-uterine) 



Fig. 41. — Ossification of the Occipital Bone. 

 (The figure shows the condition of the bone at birth.) 



the basilar portion joins the sphenoid, and at the twenty-fifth year the jugular 

 process becomes ankylosed to the petrous portion of the temporal. 



Obstetrical Hinge-Joint of Budin. — At birth the tabular or squamous portion 

 of the occipital bone is connected with the two condylar portions by a band of 

 cartilage. This region is known as the obstetrical hinge- joint of Budin. The 

 connection is such as to allow of Hmited swinging or see-saw movements in 

 front of, and behind, the cartilaginous band, by which movements the dia- 

 meters and form of the child's head are liable to be modified during labour. 



The Parietal Bones. 



The parietal bones are so named because they form a large 

 part of the cranial wall. They lie between the frontal and 

 occipital, and superiorly they articulate with each other by 

 the sagittal or interparietal suture. Each bone is quadrilateral 

 and curved, and presents two surfaces, four borders, and four 

 angles. The external surface is convex, and near its centre is more 

 elevated than elsewhere, this part, from which ossification originally 

 proceeds, being called the parietal eminence. A little below this 

 the surface is crossed from before backwards by two curved lines, 

 called the superior and inferior temporal ridges, the narrow space 

 between which is smoother and more glistening than the rest of 

 the surface. The part above the superior ridge is covered by the 

 iepicranial aponeurosis, and the ridge itself gives attachment to the 

 temporal fascia. The inferior temporal ridge limits the origin of the 



