196 



OSTEOLOGY 





length of the lateral wall of the nose, is broader in front than behind, and presents 

 anteriorly the lower orifice of the nasolacrimal canal. 



The Anterior Nasal Aperture (Fig. 181) is a heart-shaped or pyriform opening, 

 whose long axis is vertical, and narrow end upward; in the recent state it is much 

 contracted by the lateral and alar cartilages of the nose. It is bounded above by 

 the inferior borders of the nasal bones; laterally by the thin, sharp margins which 

 separate the anterior from the nasal surfaces of the maxillae ; and below by the same 

 borders, where they curve medialward to join each other at the anterior nasal 

 spine. 



The choanse are each bounded above by the under surface of the body of the 

 sphenoid and ala of the vomer; below, by the posterior border of the horizontal 

 part of the palatine bone; laterally, by the medial pterygoid plate; they are 

 separated from each other by the posterior border of the vomer. 



DIFFERENCES IN THE SKULL DUE TO AGE. 



At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion 

 is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half 

 in the adult. The frontal and parietal eminences are prominent, and the greatest width of the 



skull is at the level of the latter; on the other 



Frontal fontanel hand, the glabella, superciliary arches, and 



mastoid processes are not developed. Ossi- 

 fication of the skull bones is not completed, 

 and many of them, e. g., the occipital, temp- 

 orals, sphenoid, frontal, and mandible, consist 

 of more than one piece. Unossified mem- 

 branous intervals, termed fontanelles, are seen 

 at the angles of the parietal bones; these 

 fontanelles are six in number: two, an ante- 

 rior and a posterior, are situated in the middle 

 line, and two, an antero-lateral and a postero- 

 lateral, on either side. 



The anterior or bregmatic fontanelle (Fig. 

 197) is the largest, and is placed at the junc- 

 tion of the sagittal, coronal, and frontal 

 sutures; it is lozenge-shaped, and measures 

 about 4 cm. in its antero-posterior and 2.5 

 cm. in its transverse diameter. The posterior 

 fontanelle is triangular in form and is situated 

 at the junction of the sagittal and lambdoidal 

 sutures. The lateral fontanelles (Fig. 198) are 

 small, irregular in shape, and correspond re- 

 spectively with the sphenoidal and mastoid 

 angles of the parietal bones. An additional 

 fontanelle is sometimes seen in the sagittal 

 suture at the region of the obelion. The 

 fontanelles are usually closed by the growth 



Occipital fontanel and extension of the bones which surround 



them, but sometimes they are the sites of 



FIG. 197.-Skull at birth^showing frontal and occipital geparate ogsific centerg which dev elop into 



sutural bones. The posterior and lateral fon- 

 tanelles are obliterated within a month or two after birth, but the anterior is not completely 

 closed until about the middle of the second year. 



The smallness of the face at birth is mainly accounted for by the rudimentary condition of 

 the maxillae and mandible, the non-eruption of the teeth, and the small size of the maxillary air 

 sinuses and nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and 

 the lower border of the anterior nasal aperture is only a little below the level of the orbital floor. 

 With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these 

 changes are still more marked after the second dentition. 



The skull grows rapidly from birth to the seventh year, by which time the foramen magnum 

 and petrous parts of the temporals have reached their full size and the orbital cavities are only 

 a little smaller than those of the adult. Growth is slow from the seventh year until the approach 



