SKULL OF A HUMAN FETUS OF 40 MM. 405 



III the ectethmoid (fig. 12), as we have seen, there may be 

 recognized a roof, or tectum nasi, a lateral wall, or paries nasi, 

 and a floor, or solum nasi. Its only connections are made 

 medially with the septum (figs. 11 and 12) and laterally with the 

 cartilage sphenoethmoidalis (fig. 1), both unions being through 

 the roof. The posterior, or subcerebral portion of the tectum 

 nasi is as yet imperfectly developed, and is concerned principally 

 in the formation of the lateral deHmitation of the fenestra crib- 

 rosa, the representative of the future cribriform plate. Dorsally 

 this subcerebral portion is wide and flattened, and forms part 

 of the ventral boundary of the fissura orbitonasalis. jNIedially 

 it is connected with the nasal septum by a short line of attach- 

 ment, interrupted by small foramina (fig. 12) while laterally it 

 is bounded by the broken line of union with the cartilago spheno- 

 ethmoidalis. This portion narrows as it is followed ventrally, 

 and forms the rather uneven lateral boundary of the fenestra 

 cribrosa. 



The ventral border of this fenestra is formed by the dorsal 

 edge of the prominentia superior (fig. 1), which is a medial con- 

 tinuation of the sphenoethmoidal commissure connecting this 

 to the nasal septum in front of the crista galli. Projecting 

 backward into the fenestra cribrosa from the point of union of 

 the sphenoethmoidal commissure with the superior prominence 

 is a short spicule of cartilage, known as the processus cribroeth- 

 moidalis (fig. 1), also present in the model of Hertwig. It forms 

 the median boundary of a small incisure, known as the incisura 

 cribroethmoidalis (fig. 1) and appears to be the representative 

 of the foramen cribroethmoidale of the rabbit (Voit), through 

 which the anterior ethmoidal branch of the ophthalmic division 

 of the 5th nerve passes into the nasal from the cranial cavity, 

 to emerge, as we shall see, through the foramen epiphaniale as 

 the external nasal ramus. In the model of Hertwig the incisure 

 is still unclosed dorsally. It represents the ethmoidal fissure of 

 the mature bone. 



The ventral, or precerebral, portion of the roof is attached, 

 throughout its entire extent, to the nasal septum (fig. 12). It 



