76 



THE SKULL AS A WHOLE. 



in the fourth month, and after their union two others appear (xphenotics), 1 from which are 

 formed the lingulas and adjoining- parts of the carotid grooves. The internal pterygoid plates, 

 corresponding to the pterygoid bones of animals, are ossified from distinct nuclei, which 

 appear in the fourth month ; they unite with the external pterygoid plates in the fifth month. 

 The great wings are united to the body in the first year. 



In the presphenoid division the first pair of nuclei appears in the ninth week outside the 

 optic foramina, and extends by their growth into the small wings (orbitospfanoids) : another 

 pair of granules appears on the inner sides of the foramina, and the presphenoid portion of the 

 body either results from the union of these, or is an independent growth. The presphenoid 

 ossifications are united to the body of the postsphenoid in the seventh or eighth month. At 

 birth the place of union is marked on the under aspect of the body by a wide notch, which 

 sometimes opens above by a small hole on the olivary eminence. The body of the presphenoid 



Fig. 78. OSSIFICATION OF THE SPHENOID BONE. (E. Quain.) 



A, sphenoid bone at an early period, seen from above ; 1, 1', the greater wings ossified ; 2, 2', the 

 lesser wings, in which the ossification has encircled the optic foramen, and a small suture is distinguish- 

 able at its posterior and inner side ; 3, nuclei of basisphenoid. 



B, copied from Meckel (Archiv. vol. i, tab. vi, fig. 23), and stated to be from a foetus of six 

 months; 2*, nuclei of presphenoid; 5, separate lateral processes of the body (lingiilse) : the other 

 indications are the same as in A. 



C, back part of the bone shown in A ; 4, internal pterygoid plates still separate. 



D, sphenoid at birth. The great wings are still separate. The presphenoid is now joined to the 

 basisphenoid, and the internal pterygoid plates (not seen in the figure) are united to the external. 



is for some years broad and rounded inferiorly ; it begins to be hollowed by the sphenoidal 

 sinuses about the sixth year, and then becomes gradually narrower and more prominent, being 

 ultimately reduced to the thin sphenoidal septum. 



The spliciwidal spongy "bones begin to ossify in the fifth month. At birth each consists of 

 a small sagittal lamina, resting against the presphenoid, and continued posteriorly into a 

 lateral projection, which is hollowed in front for the sphenoidal sinus, the latter having been 

 formed as a recess of the mucous membrane of the nose at the end of the third month. By 

 the third year the bone has entirely surrounded the sinus, forming an osseous capsule with 

 an anterior opening the sphenoidal foramen. About the fourth year the upper and inner 

 parts of this capsule begin to be absorbed, and the presphenoid then forms the wall of the 

 sinus, which in its farther extension excavates the body of the bone. At the outer and fore 

 part also absorption takes place, and the cavity there comes to be bounded by the ethmoid 

 and palate bones. The anterior projections of the sagittal plates meet in front of the pre- 

 sphenoid, and uniting with the vertical plate of the ethmoid form the rostrum. The spongy 

 bones are anchylosed first to the lateral mass of the ethmoid (about the fourth year), whence 

 they are often regarded as parts of that bone. They join the sphenoid from the ninth to the 

 twelfth year. (Toldt, " Die Entstehung und Ausbildung der Conchas und der Sinus sphenoidales 

 beim Menschen," Lotos, 1882.) 



In the ethmoid bone ossification begins in the lateral masses during the fifth month, first 

 in the orbital plate, and then in the middle turbinate bone. In the first year a nucleus 

 appears in the vertical plate, and the cribriform plate is formed by ossification extending 

 from this internally and from the lateral masses externally. The three parts are united in 



1 J. B. Sutton, " On the Development and Morphology of the Human Sphenoid Bone," Proc. Zool. 

 Soc. Lond., 1885. 



