124 OSTEOLOGY. 
reached that the cancellous tissue within this part of the bone becomes absorbed to form 
the sphenoidal sinuses. 
The sphenoidal turbinals (conch sphenoidales), or bones of Bertin, best studied in 
childhood, are formed by the fusion of four distinct ossicles (Cleland), the centres for 
which appear in the later months of utero- gestation. Each bone consist of a hollow three- 
sided pyramid, the apex of which is in contact with the fore part of the vaginal process of 
the internal pterygoid, whilst the base fits on to the posterior surface of the lateral mass 
of the ethmoid. The ¢nfervor surface of each forms the roof of the corresponding nasal 
fossa and completes the formation of the spheno-palatine foramen, whilst the external 
aspect is united with the palate bone and forms the inner wall of the spheno-maxillary 
fossa and occasionally constitutes a part of the orbital wall posterior to the os planum of 
the ethmoid. The superior surface of the sphenoidal turbinal is applied to the fore and 
under surface of the body of the pre-sphenoid on either side of the rostrum. It is by the 
absorption of this wall that the sphenoidal sinuses are ultimately opened up. The base 
of the pyramid forms the aperture through which each of these sinuses opens into the 
nasal fossee in the adult. Owing to their firm ankylosis with the surrounding bones, these 
ossicles are merely represented in the adult disarticulated skull by the irregular frag- 
ments adherent to the separated borders of the ethmoid, palate, and sphenoid bones. 
THE ETHMOID BONE. 
The ethmoid bone (os ethmoidale) lies in front of the sphenoid, and oceupies 
the interval between the orbital plates of the frontal, thus entering into the forma- 
tion of the anterior cranial fossa as well as the inner walls of the orbits and the 
roof and inner and outer walls of the nasal fossee. The bone, which is extremely 
light, consists of two cellular parts—the lateral masses, which are united superiorly 
to a mesial vertical plate by a thin horizontal lamina which, from its perforated 
condition, is called the cribriform plate. 
The study of this bone will be much facilitated by cutting through the cribriform 
plate on one side of the vertical plate, thus removing the lateral mass “of one side and 
exposing more fully the central perpendicular lamina. 
fo) 
the upper part of the nasal septum. Its superior border projects above the level of 
the cribriform plate so as to form a 
erest, which is much elevated an- 
teriorly, where it terminates in a 
bullate process called the crista galli, 
the upper edge of which is sharp 
and pointed, and affords attachment 
to the falx cerebri. In front of this 
process there is a groove which 
separates the alar processes (pro- 
cessus alares) which project from 
the crista galli on either side. By 
The vertical plate (lamina perpendicularis), of irregular pentagonal shape, forms 
Alar process Crista galli 
Superior We 
turbinated~_}" ' 
bone y = 
aN 
Superior. : 
Os planum 
meatus 
Middle Opening articulation with the frontal bone 
turbinated—— ~of posterior if oOTrmove 19eA rarted 7 ¢ 
bone Cimon this groove is converted into a canal, 
cells the foramen cecum; this, however, 
g \ Uneiform is not always blind, but frequentl 
Middle meatus oe Nes Y ’ | yi 
transmits a vein to the roof of the 
nose. The posterior margin of the 
vertical plate is thin, and articulates 
with the crest of the sphenoid. 
The posterior inferior border in the adult is ankylosed with the vomer; and the 
anterior inferior edge, which is usually thicker than the others, unites with the 
cartilaginous nasal septum. The anterior superior border articulates with the nasal 
spine of the frontal bone and with the median crest formed by the union of the 
two nasal bones. The vertical plate, which is usually deflected to one or other 
side, has generally smooth surfaces, except above, where they are channelled by 
Lateral 
mass 
Perpendicular plate 
Fic. 95.—ETHMOID AS SEEN FROM BEHIND. 
