1S8 A MANUAL OF ANATOMY 



Pterion = the region of the spheno-parietal suture. 

 Rhinion-the lower part of the internasal suture. 



Stephanion = the point where the superior temporal ridge crosses the coronal 

 suture. 



Subnasal point=the centre of the base of the anterior nasal spine. 



The horizontal circumference of the cranium represents the measurement 

 at the level of a plane passing through the most prominent part of the glabella 

 in front, the pterion laterally, and the occipital point behind. 



The greatest length represents the measurement from the most prominent 

 part of the glabella to the occipital point. The greatest breadth represents 

 the transverse measurenient at the level of the most prominent parts of the 

 temporal fossae above the supramastoid crests. The proportion of greatest 

 breadth to greatest length is the index of breadth, or cephalic index. In 

 civilized races about 7 inches represents an average length, and about 5 5 inches 

 an average breadth. According to their cephalic index, skulls are arranged 

 in three classes, namely, brachycephalic (broad and short), with a cephalic 

 index over 80, as in Malays, etc. ; mesaticephalic (intermediate), with an index 

 of 75 to 80, as in Europeans and Chinese ; and dolicocephalic (long and narrow), 

 with a cephalic index below 75, as in Kaffirs and Fijians. 



The height of the skull represents the measurement from the basion to the 

 bregma, and its proportion to the length is the index of height, or vertical 

 index. Its average in civilized races corresponds with the breadth. 



The longitudinal arc of the skull represents the measurement from the 

 nasion to the opisthion carried over the roof, and the basi-nasal length repre- 

 sents the measurement from the basion to the nasion. These two measure 

 ments, plus the distance between the basion and the opisthion, represent 

 the vertical circumference of the cranium in the median plane. The degree 

 of projection of the jaws is ascertained from the gnathic or alveolar index. 

 This index represents the proportion of the basi-alveolar length to the basi- 

 nasal. According to the gnathic index, skulls are arranged in three classes, 

 namely, orthognathous (straight and upright jaw), with a gnathic index 

 below 98, as in Europeans ; mesognathous (intermediate jaw), with an index 

 of from 98 to 103, as in Chinese and Japanese ; and prognathous (forward 

 jaw), with an index over 103, as in Australians. 



The form of the anterior nasal aperture is ascertained from the nasal index. 

 This represents the proportion of the greatest transverse measurement of the 

 aperture to the height, which latter is the measurement from the nasion to 

 the subnasal point. According to their nasal index, skulls are arranged in 

 three classes, namely, leptorhine (narrow nose), with a nasal index below 48, 

 as in Europeans ; mesorhine (intermediate nose), with an index of from 48 to 

 53, as in Chinese and Japanese ; and platyrhine (broad nose), with an index 

 above 53, as in Australians and Kaffirs. 



The form of the orbital aperture is ascertained from the orbital index, which 

 re])resents the proportion of the height to the width of the orbital aperture. 

 There are three varieties of orbital index, namely, megaseme (great index), 

 when it exceeds 89, as in the Chinese ; mesoseme (intermediate index), when 

 it is between 89 and 84, as in Europeans ; and microseme (small index), when 

 it is below 84, as in Australians. 



Deformities of the Skull. 



The most common cause of cranial deformities is premature synostosis or 

 osseous union of bones which are normally separate, the result being closure 

 or obliteration of certain sutures. When the sagittal suture becomes prema- 

 turely obliterated transverse growth is arrested, and, to compensate for this, in- 

 creased growth takes place at the coronal and lambdoid sutures. The antero- 

 posterior diameter of the cranium is greatly increased, and the vault assumes 

 a boat-like shape. This variety is known as scaphocephalus. When the 

 coronal suture becomes prematurely obliterated, increased growth takes place 

 upwards, and the vertical diameter is greatly increased. Tliis variety is known 

 as acrocephalus (pointed head). When one-half of the coronal or lambdoid 

 suture becomes prematurely obliterated, obUque deformity takes place, this 



