194 



HUMAN ANATOMY. 



Fig. 219. 



Probe in infundibulum 



naso-turbinal bone of many mammals. Behind this is a globular swelling, the bulla,^ 

 formed by a plate springing from the os planum, covering cells, which also is held 

 to represent a turbinate. Between the uncinate process and the bulla is a deep 

 groove, the i7ifu?idibzihi?n* curving downward and backward, the opening into which 

 irom the nasal fossa is known as the hiatus semilmiaris. The upper end of the 



, infundibulum opens into 



the frontal sinus in about 

 half the cases, ^ ending 

 blindly in the others ; it 

 is bounded externally to 

 a varying extent by the 

 lachrymal. A number 

 of anterior ethmoidal 

 cells generally open into 

 this portion. The upper 

 part of the infundibu- 

 lum has an opening on 

 its outer side into the 



Crista galli 



Cribriform- 

 plate 



Sup. turbinate 

 Sup. meatus 



Middle tur- 

 binate 



Uncinate process 



Bulla 



The ethmoid bone, inner aspect from left side, part of the middle turbinate 



having been removed. 



antrum. 



Articulations. — 



Xhese have already been 

 described incidentally. 

 Briefly recapitulated^ 

 however, the articula- 

 tions of the ethmoid are 

 with the frontal, the 

 sphenoid, the palatals, the vomer, the inferior turbinates, the lachrymals, and the 



nasals. 



Development. — The ethmoid is very small at first and backward in its 

 development. About the middle of foetal life ossification appears in the os planum 

 and the middle turbinate bone. A centre (two, according to Poirier) for the vertical 

 plate occurs in the first year, from which ossification extends into the crista galli. 

 The cribriform ossifies chiefly (perhaps wholly) from the lateral masses. The date 

 of the union of the three pieces is rather uncertain ; it takes place, probably, at 

 about the sixth year. The cells appear first as depressions during foetal life. 

 According to the more generally accepted view, their growth is by absorption of 

 bone. It is hard to believe that this is not, at least, a factor ; Poirier, however, 

 holds that they are due to the course of ossification. 



THE FRONTAL BONE. 



This bone,* which forms the front of the vault of the skull, most of the floor of 

 its anterior fossa, and bounds the greater part of the orbits and the ethmoidal cells 

 above, is developed into two symmetrical halves which unite in the second year. It 

 is convenient to divide the bone thus formed into a vertical and a horizontal portion, 

 although this division rests on no scientific basis. 



The vertical portion,'^ convex anteriorly, presents on either side, below its 

 middle, the fro7ital eminence,^ which represents the chief centre of ossification -f 

 either half. Very prominent in infancy, it diminishes during growth, and is hardly 

 to be made out in most adult skulls. The lower border of the vertical portion grows 

 downward in front between the orbits. At the sides of this projection are the 

 internal angular processes of the orbits. In the middle-line a faint zigzag line marks 

 the remnant of the interfrontal snture. Above this is a smooth, rather prominent 

 surface, called the glabella, external to which are the superciliary ridges,"^ or emi- 

 nences, which extend outward, somewhat above the inner ends of the orbits. The 

 development of these varies greatly. On either side of the nasal projection is the 

 orbital arch, extending outward from the internal angular process. At about the 

 *H. A. I^othrop : Annals of Surgery, vol. xxviii., 1898. 



'Bulla ethmoidalis. ^ Infundibulum ethmoidale. ^Os frontale. ^Squama frontalis. * Tuber frontale. 'Arc 

 eaperciliares. 



