64 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



teeth. There may be two dental canals. The angle of the 

 jaw in the adult is about 120 degrees; in infancy, 140 degrees 

 or more; in old and toothless jaws, it is increased. These 

 changes are due to development, absorption of the alveolar 

 arch, and strength of the masseter muscles. 



The Skull as a Whole 



THE SUTURES OF THE SKULL 



The skull bones are closely fitted by uneven edges, there 

 being interposed a little fibrous tissue continuous with the 

 periosteum; the dentations are confined to the external table, 

 the edges of the inner table lying only in apposition. The 

 lower jaw-has a movable articulation, differing from the others. 

 The sutures around three sides of the parietal bones have 

 special names between the two is the sagittal, behind them 

 the lambdoid, in front of them the coronal. 



All the sutures may be arranged in three groups a -median 

 longitudinal, a lateral longitudinal, and a vertical //Y///.W/-.SV. 

 The first consists of the sagittal, and in the infant the frontal; 

 the second begins in the median line in front, and includes 

 on each side the frontonasal, frontomaxillary, frontolacry- 

 mal, frontoethmoidal, frontomalar, frontosphenoidal, spheno- 

 parietal, squamoparietal, and mastoparietal ; the third comprises 

 the coronal and sphenosquamous, the lambdoid and occipito- 

 mastoid, and also the transverse sutures at the base of the 

 skull. 



After about thirty years of age many sutures close, union 

 taking place on the inner surface first; the parts to close first 

 are the sagittal suture between the parietal foramina and 

 the lower ends of the coronal suture. 



Wormian Bones. These ossa triquetra, ossa suturarum, 

 are irregular ossifications between cranial bones rarely found 

 in the face. They are usually symmetrical, and are most 

 common in the lambdoid suture, occupying the place of the 

 superior angle of the occipital bone; may be at either anterior 

 angle of the parietals. They usually include only one plate 

 of the skull. 



