198 OSTEOLOGY 



In comparing the shape of one skull with that of another it is necessary to adopt some definite 

 position in which the skulls should be placed during the process of examination. They should 

 be so placed that a line carried through the lower margin of the orbit and upper margin oi' the 

 external acoustic meatus is in the horizontal plane. The normse of one skull can then be com- 

 pared with those of another, and the differences in contour and surface form noted. Further, 

 it is necessary that the various linear measurements used to determine the shape of the skull 

 should be made between definite and easily localized points on its surface. The principal points 

 may be divided into two groups: (1) those in the median plane, and (2) those on either side of it. 



The Points in the Median Plane are the: 



Mental Point. The most prominent point of the chin. 



Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar 

 arch. 



Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the base 

 of the anterior nasal spine. 



Nasion. The central point of the frontonasal suture. 



Glabella. The point in the middle line at the level of the superciliary arches. 



Ophryon. The point in the middle line of the forehead at the level where the temporal lines 

 most nearly approach each other. 



Bregma. The meeting point of the coronal and sagittal sutures. 



Obelion. A point in the sagittal suture on a level with the parietal foramina. 



Lambda. The point of junction of the sagittal and lambdoidal sutures. 



Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. 



Inion. The external occipital protuberance. 



Opisthion. The mid-point of the posterior margin of the foramen magnum. 



Basion. The mid-point of the anterior margin of the foramen magnum. 



The Points on Either Side of the Median Plane are the: 



Gonion. The outer margin of the angle of the mandible. 



Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal 

 bone and the frontal process of the maxilla. 



Stephanion. The point where the temporal line intersects the coronal suture. 



Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the 

 parietal. 



Auricular Point. The center of the orifice of the external acoustic meatus. 



Asterion. The point of meeting of the lambdoidal, mastooccipital, and mastoparietal sutures. 



The horizontal circumference of the cranium is measured in a plane passing through the glabella 

 (Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 

 50 cm. in the female and 52.5 cm. in the male. 



The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the 

 vertex to the opisthion: while the basinasal length is the distance between the basion and the 

 nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, 

 represent the vertical circumference of the cranium. 



The length is measured from the glabella to the occipital point, while the breadth or greatest 

 transverse diameter is usually found near the external acoustic meatus. The proportion of 



breadth to length is termed the cephalic index or index of breadth. 



length 



The height is usually measured from the basion to the bregma, and the proportion of height 



, (height X 100) 



to length constitutes the vertical or height index. 



length 



In studying the face the principal points to be noticed are the proportion of its length and 

 breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection 

 of the jaws. 



The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible 

 be wanting, to the alveolar point; while its width is represented by the distance between the 

 zygomatic arches. By comparing the length with the width of the face, skulls may be divided 

 into two groups; dolichofacial or leptoprosope (long faced) and brachy facial or chemoprosope (short 

 faced). 



The orbital index signifies the proportion which the orbital height bears to the orbital width, 

 thus: 



orbital height X 100 



orbital width 



The nasal index expresses the proportion which the width of the anterior nasal aperture bears 

 to the height of the nose, the latter being measured from the nasion to the lower margin of the 

 nasal aperture, thus: 



nasal width X 100 



nasal height 



