FRONTAL BONE. 



63 



Fig. 26 * 



lead into the frontal sinuses ; and between the two internal angular pro- 

 cesses, is a rough excavation which receives the nasal bones, and a pro- 

 jecting process, the nasal spine. Upon each orbital plate, immediately 

 beneath the external angular process, is a shallow depression which lodges 

 the lachrymal gland ; and beneath the 

 internal angular process a small pit, 

 sometimes a tubercle, to which the 

 cartilaginous pulley of the superior 

 oblique muscle is attached. 



Internal Surface. Along the mid- 

 dle line of this surface is a grooved 

 ridge, the edges of the ridge giving 

 attachment to the falx cerebri and the 

 groove lodging the superior longitu- 

 dinal sinus. At the c6mmencement 

 of the ridge is an opening, sometimes 

 completed by the ethmoid bone, the 

 foramen caecum. This opening lodges ( 

 a process of the dura mater, and oc- 

 casionally gives passage to a small 

 vein which communicates with the 

 nasal veins. On each side of the vertical ridge are some slight depres- 

 sions which lodge the glandulse Pacchioni, and on the orbital plates a 

 number of irregular pits called digital fosses, which correspond with the 

 convolutions of the anterior lobes of the cerebrum. The superior border 

 is thick and strongly serrated, bevelled 

 at the expense of the internal table in 

 the middle, where it rests upon the 

 junction of the two parietal, and at the 

 expense of the external table on each 

 side where it receives the lateral pres- 

 sure of those bones. The inferior bor- 

 der is thin, irregular, and squamous, 

 and articulates with the sphenoid 

 bone. 



Development. By two centres, one 

 for each lateral half. Ossification be- 

 gins in the orbital arches, somewhat 

 before the vertebrae. The two pieces 

 are separate at birth, and unite by su- 

 ture during the first year, the su- 

 ture sometimes remaining permanent 



* The external surface of the frontal bone. 1. The situation of the frontal eminence 

 of the right side. 2. The superciliary ridge. 3. The supra-orbital ridge. 4. The ex 

 ternal angular process. 5. The internal angular process. 6. The supra-orbital notch 

 for the transmission of the supra-orbital nerve and artery; in the figure it is almost 

 converted into a foramen by a small spiculum of bone. 7. The nasal tuberosity; the 

 swelling around this point denotes the situation of the frontal sinuses. 8. The temporal 

 ridge, commencing from the external angular process (4). The depression in yhicii 

 the figure 8 is situated is a part of the temporal fossa. 9. The nasal spine. 



f- The internal surface of the frontal bone ; the bone is raised in such a manner as to 

 chow the orbito-nasal portion. 1. The grooved ridge for the lodgment of the superior 

 longitudinal sinus and attachment of the falx. 2. The foramen ciecum. 3. The superior 



