The development of the human body; a manual of human embryology . uite separate from one another, theolfactory and nasal nerves passing down between them to the olfactory pit, but laterbony trabecular begin to ex-tend across from the junctionbetween the crista galli andperpendicular plate to theupper part of the ectethmoidsand eventually form a fenes-trated horizontal lamella, thecribriform plate. The lower part of the me-dian cartilage does not ossify,but a center appears on eachside of the median line in themesenchyme behind and be-low its posterior or lower bor-der. From these centers twove
The development of the human body; a manual of human embryology . uite separate from one another, theolfactory and nasal nerves passing down between them to the olfactory pit, but laterbony trabecular begin to ex-tend across from the junctionbetween the crista galli andperpendicular plate to theupper part of the ectethmoidsand eventually form a fenes-trated horizontal lamella, thecribriform plate. The lower part of the me-dian cartilage does not ossify,but a center appears on eachside of the median line in themesenchyme behind and be-low its posterior or lower bor-der. From these centers twovertical bony plates developwhich unite by their median surfaces below, and aboveinvest the lower border of the cartilage and form thevomer. The portion of the cartilage which is thus investedundergoes a certain amount of resorption, but the moreanterior portions persist to form the cartilaginous septumof the nose. The vomer, consequently, is, not really aportion of the chondrocranium, but is a membrane bone;its intimate relations with the median ethmoidal carti-. Fig. 103.—Anterior Portionop the Base op the Skullof a 6 to 7 Months Em-bryo. The shaded parts represent car-tilage, cp, Cribriform plate;Im, lateral mass of the eth-moid ; lp, perpendicular plate;of, optic foramen; os, orbito-sphenoid.—{After von Spee.) THE SKULL. 199 lage, however, make it convenient to consider it in thisplace. When first formed, the ectethmoids are masses ofspongy bone and show no indication of the honeycombedappearance which they present in the adult skull. Thiscondition is produced by the absorption of the bone ofeach mass by evaginations into it of the mucous mem-brane lining the nasal cavity. This same process alsobrings about the formation of the curved plates of bonewhich project from the inner surfaces of the lateralmasses and are known as the superior and middle turbin-ated bones. The inferior and sphenoidal turbinatedbones are developed from special centers but belong to thesame categor
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
