GENERAL DEVELOPMENT OF THE SKULL, 221 



posterior to the cuneiform process is the foramen magnum, and 

 behind this is the occipital surface which presents two large 

 fossce for lodging the lobes of the cerebellum. These are sepa- 

 rated by a vertical ridge, to which ihefalx minor is attached. 

 Where the vertical and transverse ridges intersect, is seen 

 the internal occipital protuberance, corresponding to the sit- 

 uation of the torcular Heropliili, or the common point of 

 junction of the great sinuses of the brain. 



On either side of this protuberance is the transverse ridge 

 to which the tentorium is attached, and below and parallel 

 with this ridge is a deep groove which is continued along 

 the inferior angles of the parietal and the mastoid portion 

 of the temporal bone, and finally end in the foramen lacerum 

 posterius of each side. This groove conducts the lateral 

 sinuses out of the brain, 



GENERAL DEVELOPMENT OF THE SKULL. 



In the foetus, the upper part of the face decidedly pre- 

 dominates, in consequence of the early development of the 

 frontal bone. The middle portion or upper jaw is, on the 

 other hand, very small from the absence of the maxillary 

 sinus so that the floor of the orbit and the alveolar arch 

 almost meet. The alveolar border is prominent, owing to 

 the presence of the germs of the teeth. 



The lower portion of the face, consisting of the lower 

 jaw, is also, at this period, contracted in its vertical diam- 

 eter, and like the upper maxilla, from the presence of teeth 

 germs, presents a similar prominence in its alveolar arch. 

 The ethmoid bone is also, at this period, little developed 

 in height. The transverse diameter of the face, on a line 

 with the orbits, is great ; at the lower part, small. 



In the adult, the maxillary sinuses being developed, and 

 the alveolar arches being widened and extended, give the 

 face the characteristic expression of this period of life; 

 while in the aged, the loss of the alveolar processes and 

 teeth brings back again the face in a great measure to the 

 foetal condition. These remarks apply mostly to the ante- 

 rior face. The posterior or guttural portion in the foetus and 



