96 



SPECIAL ANA TOMY OF THE SKELETON 



the sphenoidal turbinated processes make their appearance about the fifth month. At birth they 

 consist of small triangular laminae, and it is not until the third year that they become hollowed out 

 and cone-shaped. About the fourth year they become fused with the lateral masses of the 

 ethmoid, and between the ninth and twelfth years they unite with the sphenoid bone. 



The presphenoid is united to the body of the postsphenoid about the eighth month, so that at 

 birth the bone consists of three pieces viz., the body in the centre, and on each side the great 

 wings with the pterygoid processes. The lesser wings become joined to the body at about the 

 time of birth. During the first year after birth the greater wings and body are united. From 

 the ninth to the twelfth year the turbinated processes are partially united to the sphenoid, their 

 junction being complete by the twentieth year. Lastly, the sphenoid joins the occipital from the 

 eighteenth to the twenty-fifth year. 



Articulations. The sphenoid articulates with all the bones of the cranium, and five of the 

 face the two malar, the two palate, and vomer; the exact extent of articulation with each bone 

 is shown in the accompanying figures. 1 



Attachment of Muscles. To eleven pairs the Temporal, External pterygoid, Internal 

 pterygoid, Superior constrictor, Tensor palati, Levator palpebrae, Superior oblique, Superior 

 rectus, Internal rectus, Inferior rectus, External rectus. 



The Ethmoid Bone (Os Ethmoidale) . 



The ethmoid is an exceedingly light, spongy bone, of a cubical form, situated 

 at the anterior part of the base of the cranium proper, between the two orbits 



at the root of the nose, and 

 contributing to the formation 

 of each of these cavities. It 

 consists of three parts a 

 horizontal plate, which forms 

 part of the base of the cra- 

 nium proper; a perpendicular 

 plate, which forms part of the 

 septum of the nose; and two 

 lateral masses, containing a 

 number of spaces. 



The Horizontal Lamina, 

 or Cribriform Plate (lamina 

 cribrosd) (Fig. 62), forms part 

 of the anterior fossa of the 

 base of the skull, and is re- 

 ceived into the ethmoid notch 

 of the frontal bone between 



With inferior turbinated bone. 



FIG. 62. Ethmoid bone 



Outer surface of right lateral mass. 

 (Enlarged.) 



the two orbital plates. Pro- 

 jecting upward from the middle line of this plate is a thick, smooth, triangular 

 process of bone, the crista galli. Its base joins the cribriform plate. Its posterior 

 border, long, thin, and slightly curved, serves for the attachment of the falxcerebri. 

 Its anterior border, short and thick, articulates with the frontal bone, and presents 

 two small projecting alae (processus alares), which are received into corresponding 

 depressions in the frontal, completing the foramen cecum behind. Its sides are 

 smooth and sometimes bulging, in which case it is found to enclose a small sinus. 

 On each side of the crista galli the cribriform plate is narrow and deeply grooved, 

 to support the bulb of the olfactory tract, and is perforated by foramina for the 

 passage of the olfactory nerves. These foramina are arranged in three rows: 

 The innermost, which are the largest and least numerous, are lost in grooves on the 

 upper part of the septum; the foramina of the outer row are continued on to the 

 surface of the superior turbinated process. The foramina of the middle row 



1 It also sometimes articulates with the tuberosity of the maxilla. 



