These thin anterior coverings of the sphenoidal sinuses, often termed concha sphenoidales or bones 0}Berlin, are found as a rule attached to the sphenoid, but as they are developed as ossifications associated with the posterior cupola of the cartilaginous nasal capsule, quite distinctly separate from the sphenoid, they are considered separately here. Each bone fits as a cap on the front of the corresponding sinus and presents a rounded opening above the centre of its anterior surface : the outer and lower corner of this surface is prolonged outwards and downwards with a sharp angle, and the whole surface is applied to the back of the ethmoid.
The lower aspect is separated from its fellow by the projection of the rostrum, and forms a point which fits in between the rostrum and the internal pterygoid plate. The inner, upper and outer parts of the bone are applied to and fused with the sphenoidal septum and upper and outer parts of the body of the sphenoid respectively. The lower surface appears in the roof of the nasal fossa, and, outside this, articulates with the palate bone and forms the upper boundary of the spheno-palatine foramen : the outer surface is in the inner wall of the orbit between the ethmoid and the presphenoid. ,
Each bone is usually destroyed in part during disarticulation owing to its adhesion to the neighbouring bones : a fairly complete specimen is shown on one side in Fig. 183.
Each ossicle commences to ossify in the fifth month by a centre on the innner part of the cartilaginous cupola of the nasal capsule, followed about a couple of months later by a second centre on the outer part. These centres form the bone by fusion with each other and with additional lower centres in the first year or so of life. During the fourth and fifth year the cartilaginous structure is absorbed, and this absorption extends to the outer and back part of the bony structure, so that the commencing sphenoidal sinus comes into relation with the sphenoid, into which it commences to extend about the seventh year. The bones are not fused with the sphenoid until the cartilage is absorbed.