16 



Sulcus sagittalis 



/Fades cerebralis 



Squama 

 Iroulalis 



Pars orbitalis 



Foramen caecum Processus xygomaticus 



Spina frontalis 



Pars nasalis 



17. Frontal bone, os fronlale, from behind. 



The concave posterior surface of the squama frontalis (see also Figs. 6266) forms a 

 part of the fades cerebralis (0. T. internal surface) of the frontal bone. In the median plane 

 in the upper part, is a shallow groove, sulcus sagittalis (for the sinus sagittalis superior; 

 falx cerebri); out of its lower end develops a narrow, usually markedly projecting sharp ridge, 

 the frontal crest or crista frontalis (for the falx cerebri), which, below, forms the anterior 

 boundary of the foramen caecum. Shallow juga cerebralia and impressiones digitatae are 

 visible, chiefly in front, below and behind. 



The term pars nasalis (see also Figs. 16, 18, 5558, and 73 75) is applied to the 

 part projecting somewhat from the inferior margin of the squama frontalis in the middle; it 

 separates the two partes orbitales from one another. In front it is bounded by the slightly 

 serrated mar go nasalis, to which the nasal bone is attached on each side (sutura nasofrontalis) ; 

 immediately adjacent is attached the proc. frontalis maxillae (sutura frontomaxillaris). The 

 posterior free margin is the anterior part of the incisura ethmoidalis ; it unites with !he 

 anterior margin of the lamina cribrosa oss. ethmoidalis and forms a part of the sutura fronto- 

 ethmoidalis. Obliquely downward and forward from the inferior rough surface projects the 

 spina frontalis (0. T. nasal spine). It is rough in front for the further attachment of the 

 nasal bones and of the frontal processes of the maxillae; its posterior, partly smooth, partly 

 rough, surface is applied median ward to the crista galli and lamina perpendicularis oss. ethmoidalis, 

 lateralward to the medial wall of the ethmoidal labyrinth ; between these the posterior surface 

 helps to form also the anterior wall of the nasal cavity. On the upper surface, close behind 

 the inferior extremity of the crista frontalis, lies the entrance (usually formed by the frontal 

 bone alone) to the foramen caecum, a canal which grows smaller as it descends and ends 

 blindly in the apex of the spina frontalis ; it contains only a process of the dura mater. The 

 spina frontalis is also perforated by a small canal which extends from behind and above, 

 forward and downward, and gives passage to the n. ethmoid, ant.. 



