156 



)LOGY 





The medial surface of the labyrinth (Fig. 153) forms part of the latera) wall 

 of the corresponding nasal cavity. It consists of a thin lamella, which descends 

 from the under surface of the cribriform plate, and ends below in a free, convoluted 

 margin, the middle nasal concha. It is rough, and marked above by numerous 

 grooves, directed nearly vertically downward from the cribriform plate; they 

 lodge branches of the olfactory nerves, which are distributed to the mucous mem- 

 brane covering the superior nasal concha. The back part of the surface is sub- 

 divided by a narrow oblique fissure, the superior meatus of the nose, bounded above 

 by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells 

 open into this meatus. Below, and in front of the superior meatus, is the convex 

 surface of the middle nasal concha; it extends along the whole length of the medial 

 surface of the labyrinth, and its lower margin is free and thick. The lateral surface 

 of the middle concha is concave, and assists in forming the middle meatus of the 

 nose. The middle ethmoidal cells open into the central part of this meatus, and a 

 sinuous passage, termed the infundibulum, extends upward and forward through 

 the labyrinth and communicates with the anterior ethmoidal cells, and in about 

 50 per cent, of skulls is continued upward as the frontonasal duct into the frontal 

 sinus. 



Ossification. The ethmoid is ossified in the cartilage of the nasal capsule by three centers: 

 one for the perpendicular plate, and one for each labyrinth. 



The labyrinths are first developed, ossific granules making their appearance in the region of 

 the lamina papyracea between the fourth and fifth months of fetal life, and extending into the 

 conchse. At birth, the bone consists of the two labyrinths, which are small and ill-developed. 

 During the first year after birth, the perpendicular plate and crista galli begin to ossify from a 

 single center, and are joined to the labyrinths about the beginning of the second year. The 

 cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. 

 The development of the ethmoidal cells begins during fetal life. 



Articulations. The ethmoid articulates with fifteen bones: four of the cranium the frontal, 

 the sphenoid, and the two sphenoidal concha?; and eleven of the face the two nasals, two maxilte, 

 two lacrimals, two palatines, two inferior nasal conchae, and the vomer. 



Sutural or Wormian 1 Bones. In addition to the usual centers of ossification of the cranium, 

 others may occur in the course of the sutures, giving rise to irregular, isolated bones, termed 

 sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, 

 but are occasionally seen at the fontanelles, especially the posterior. One, the pterion ossicle, 

 sometimes exists between the sphenoidal angle of the parietal and the great wing of the sphenoid. 

 They have a tendency to be more or less symmetrical on the two sides of the skull, and vary 

 much in size. Their number is generally limited to two or three; but more than a hundred have 

 been found in the skull of an adult hydrocephalic subject. 



THE FACIAL BONES (OSSA FACIEI). 



The Nasal Bones (Ossa Nasalia) . 



The nasal bones are two small oblong bones, varying in size and form in different 

 individuals; they are placed side by side at the middle and upper part of the face, 

 and form, by their junction, "the bridge" of the nose (Fig. 190). Each has two 

 surfaces and four borders. 



Surfaces. The outer surface (Fig. 155) is concavoconvex from above downward, 

 convex from side to side; it is covered by the Procerus and Compressor naris, and 

 perforated about its center by a foramen, for the transmission of a small vein. 

 The inner surface (Fig. 156) is concave from side to side, and is traversed from above 

 downward, by a groove for the passage of a branch of the nasociliary nerve. 



Borders. The superior border is narrow, thick, and serrated for articulation with 

 the nasal notch of the frontal bone. The inferior border is thin, and gives attach- 



1 Ole Worm, Professor of Anatomy at Copenhagen, 1624-1639, was erroneously supposed to have given the first 

 detailed description of these bones. 



