THE BONES. 51 



a. The papyraceous plate, bounded above by the frontal bone, incisurte 

 ethmoidaks (foramina orbitalid) ; before by the lacrymal bones, below by the 

 upper jaw, behind by the palate and sphenoid. 



b. The nasal plate is divided by a horizontal fissure into a superior (poste- 

 rior) shell (concha Morgagni), and a central (concha media'), and larger. Both 

 externally concave. Sometimes there are three shells or conchae. 



c. Sinus seu celluke ethmoidales, with a transverse septum passing through. 



a. Anterior, cell, lachrymales, opening with the frontal sinuses, below the 

 middle concha (Infundibulum, meatus nasalis medius). Larger and more 

 numerous than 



b. Posterior, cell. palatinaR; opening, with the sphenoidal cells, below the 

 superior concha ; they are separated from the sphenoid bone by the Cornua 

 Bertini. The cells are lined with a delicate periosteum and ciliated epithe- 

 lium, not mucous membrane. 



From the anterior cells, on the inferior anterior border of the papyraceous 

 plate, a hook passes off, Process, wncinatus, which unites with the concha in- 

 ferior. 



Conjunctions of the ethmoid with thirteen bones : frontal, 

 sphenoid, the inferior turbinate, upper jaw, nasal, lacrymal, palate 

 bones, and Vomer. 



Development. Ossification commences at the fifth month, first in the papy- 

 raceous plates, then in the conchae ; in the sixth to the twelfth month after 

 birth, in the Crista Galli and lamina perpendicularis, the most anterior part of 

 which, septum mobile of the nose, remains during life cartilaginous. The 

 cribriform plate is first completely ossified in the second to the third year, 

 the cells are first developed completely in the fifth to the sixth year ; in the 

 mature foetus the external and internal lateral walls lie close to one another. 



50. 4. Os frontah, s. coronate, forehead bone. 



Situation. At the most anterior part of the skull over the face. 



Shape: of a shell; the superior, larger and vaulted portion, p. 

 frontalis, vertical, the inferior, paries orbitales, horizontal. 



Conjunctions with twelve bones ; two parietal, one sphenoid, 

 one ethmoid, two nasal, two malar, two lacrymal, two superior 

 maxillary bones. 



a. Pars frontalis, forming the forehead, perpendicular and gently vaulted, 

 unites at its superior border (m. coronalis) with the parietal bones, in the 

 coronal suture ; the inferior edge limits the horizontal part anteriorly. Two 

 surfaces. 



1. External, convex, with the frontal suture in the first year, a frontal 

 prominence, tuber frcmtale, the centre of ossification on either side ; under this 

 the arch of the eyebrow, arcus superciliares (for the muse, corrugator superdlii) ; 

 between them the triangular smooth surface Glabetta, and below them mar- 

 gines supraorbitaks, superior border of the orbit (for the m. orbiculares palpebra- 

 ntm), with Indsura or foramen supraorbitak (for the nerv. art. and ven. supra- 

 orbitales), and externally Process, zygomaticus (uniting with the malar bone), 

 above Crista frontalis, and in continuation linea semicircularis (for the muse, 

 tempor alts'). 



2. Internal, concave surface j besides the elevations and depressions for the 



