SKULL OF A 43-MM. HUMAN FETUS. 



79 



angle of the greater wing. It is inclosed in con- 

 densed mesenchyme, which is continuous with 

 that enveloping the palate bone, as seen in figures 

 28, 30, and 41. 



ORBITAL WING. 



The orbital or lesser wings of the sphenoid are 

 seen from above, below, in front, and from the 

 side in figures 1, 2, 3, and 5, respectively. The 

 two wings make with one another an angle of 

 131°, measuring from the upturned tips of the 

 dorsolateral processes and limbus sphenoidalis. 

 The corresponding angle was measured in four 

 adult skulls and found to range from 147.5° to 

 154.5°, the average being 150°. 



The wings have been described by many authors 

 as sickle-shaped plates of cartilage joined medially 

 to the presphenoid and anteriorly continued as 

 the sphenoethmoidal cartilage. It is convenient 

 to divide each wing into four parts: the body, the 

 dorso-lateral process, and the two roots. The 

 body is thin and almost plane anteriorly, while 

 posteriorly it is thicker and narrower. It is this 

 latter portion of the wing which is the first to 

 develop, according to the accounts of earlier 

 stages, as that of Lewis (1920), where the shape is 

 also that of a sickle, but with the concavity of the 

 blade directed inward to form the boundary of the 

 optic foramen. The anterior root, in No. 460, 

 has not joined with the main stem and in No. 88G 

 it has evidently just joined, for it is very slender 

 and of young cartilage. Lateral to the optic 

 foramina, the upper surface of the body shows a 

 gentle concavity upward and inward (fig. 1) and 

 below this region there is a corresponding con- 

 vexity downward. When seen from the side 

 (figs. 5, 6) the combined lesser wings and spheno- 

 ethmoidal cartilages present a distinct concavity 

 downward, this plate of cartilage forming part of 

 the roof of the orbit. The anterior border of 

 the body forms the caudal boundary of the orbito- 

 nasal fissure— a triangular cleft which partially 

 separates the wing from the sphenoethmoidal 

 cartilage. The lateral border of the two plates, 

 beginning in front at the spheno-ethmoidal com- 

 missure, describes a compound curve, the edge of 

 the spheno-ethmoidal cartilage showing a strong 

 outward convexity, which is followed by a gentle 

 outward concavity as the line passes over upon the 

 dorsolateral process. Just beyond this border 

 is the posteromedial edge of the frontal bone. 



The posterior border, beginning at the inner 

 extremity of the superior orbital fissure, also 

 describes a compound curve, the first portion of 

 which is very sharply convex backward, where it 



passes around the pointed anterior clinoid process; 

 there is next a long sweeping curve with concavity 

 backward, the first portion of which shows a 

 thickened margin. 



The dorsolateral process is an almost straight 

 cylindrical rod pointed backward, outward, and 

 upward, and is somewhat thicker than the portion 

 of the wing from which it springs. 



The posterior root of the lesser wing is a short, 

 stout rod of cartilage which springs laterally 

 from the tuberculum sellae (fig. 10). Each root 

 shows a rather wide, shallow groove upon the 

 dorsal surface, that on the right side being slightly 

 better marked. A narrower groove is found upon 

 the ventral surface of each root, which is con- 

 tinued forward as the groove separating the ala 

 hypochiasmatica from the medial stem. From 

 the anterior aspect of the junction of root and 

 presphenoid, the ala hypochiasmatica is continued 

 forward. The anterior clinoid processes are 

 rather blunt and tipped with young cartilage. 



Lewis (1920, p. 309) surmises that there are 

 separate centers of chondrification for the two 

 parts of the orbital wing, the basal and the 

 lateral — a point which was advanced by Kernan 

 (1916), who identified the "basal part" as the ala 

 hypochiasmatica. Lewis thinks that the basal 

 part is later incorporated into the sphenoidal body. 



The anterior roots of the ala orbitalis, formed of 

 young cartilage, are very slender. In la they 

 were very much wider and stouter. 



Optic foramen. — But little remains to be said as 

 to the optic foramen. The lateral border, which 

 may be considered to be formed by the margins 

 of the body and the two roots, is semicircular 

 in outline and lies at a higher level than the medial, 

 which is made anteriorly by the prechiasmatic 

 commissure and posteriorly by the outer margin of 

 the hypochiasmatic lamina, bearing the salient 

 hypochiasmatic wings. 



The triangular spheno-ethmoidal cartilage (figs. 

 1, 5, 6) is confluent caudally with the lesser wing 

 of the sphenoid. Its cranio-ventral angle is con- 

 nected with the projecting upper edge of the 

 ectethmoid by a narrow bridge, the spheno- 

 ethmoidal commissure, and behind this the con- 

 nection with the ectethmoid along the inner bor- 

 der of the cartilage is accomplished by several 

 cartilaginous strands. This connection is very 

 imperfect caudally. Most of the caudal border — 

 that medial to the connection with the orbito- 

 sphenoid — is free, forming the cranial limit of the 

 orbitonasal fissure. The medial part of this bor- 

 der is irregular, and marked by projections of 

 young cartilage into the fissure. The part of the 



