SKULL OF A HUMAN FETUS OF 40 MM. 393 



lamina, in which is found, among other structures, the optic 

 chiasma. 



The optic foramen is pear-shaped in outhne, with the narrow 

 end ventro-medial. The lateral border is somewhat higher than 

 the medial, and is downwardly and inwardly concave. The 

 optic nerve and ophthalmic artery may be seen to pass through it, 

 the former overlying the latter. 



The ventralmost portion of the orbital wing has been known 

 by the name of cartilago sphenoethmoidalis. This is a triangu- 

 lar plate of cartilage, somewhat thinner than that composing 

 the remainder of the wing, and showing ventrally a connection 

 with the superior prominence of the lateral nasal cartilage 

 through the sphenoethmoidal commissure (fig. 1), and dorsal to 

 this connections at several points with the lateral nasal cartilage 

 as far back as the orbitonasal fissure, the bonds of attachment 

 being broken by intervening foramina. Thus there is formed 

 here a secondary, lateral cribriform plate, similar to that shown 

 in the model of Hertwig, which leads from the anterior cranial 

 fossa, not iato the nasal capsule, but into the orbit. The dorsal 

 margin is irregular and forms the outer half of the ventral margin 

 of the orbitonasal fissure, the medial half being formed by the 

 dorsal surface of the ectethmoid. 



The ventral border . of the orbitonasal fissure is somewhat 

 lower than the dorsal. The fissure is elongated, its long dimen- 

 sion being directed laterally, and in this it differs from the con- 

 dition shown in the skull of lepus (Voit) , where it is directed 

 ventro-laterally. In the latter animal, too, there are no con- 

 nections with the ectetlimoid dorsal to the sphenoethmoidal 

 commissure. As in the skull of lepus (Voit) so in man, the 

 fissure is principally filled with connective tissue, but in its 

 ventral region it transmits the anterior ethmoidal nerve and 

 vessels from the orbit to the anterior cranial fossa. It is thus, 

 in this region, representative of the anterior ethmoidal foramen 

 of the adult, skull. 



The lateral border of the ala orbitalis is serrated, and passes 

 directly backward and outward to terminate in the hornlike, 

 dorso-lateral process (fig. 1). It overlies, except at its tip, the 



