SKULL OF A HUMAN FETUS OF 40 MM. 403 



cartilage when it disappears, although the vomer is present 

 along with the cartilago paraseptalis communis in the skull of 

 the rabbit (Voit). It appears evident from a study of my slides 

 that the vomer attains its adult condition by advancing upward 

 in this sheet of mesenchyme, and thus comes to enclose the sep- 

 tum. What part, if any, the superior paraseptal cartilages 

 play in the development of the vomer, or indeed what their real 

 significance is, I am unable to say. 



At the ventral end of the caudal border of the mesethmoid, 

 and lying almost parallel with it, there are to be seen, upon either 

 side, the small, straight, rod-like ventro-lateral processes (figs. 2, 

 3 and 18), 9 mm. in length in the model, connected by their ven- 

 tral extremities with the septum (fig. 11), but having their dorsal 

 ends free, the greater part of their length being separated from 

 the septum by perichondrium. The condensed mesen-^hyme of the 

 ventral tip of the maxilla appears immediately beneath them (f gs. 



2 and 18), and their material is cartilage of the same character 

 as that of the adjacent septum. Though their dorsal extremi- 

 ties come into close contact with the cranio-ventral pro:'ess 

 of the median Jacobsoni9,n cartilage, they are not connected 

 therewith. 



The Jacobsonian or anterior paraseptal cartilages (figs. 2, 



3 and 18) consist of two paired masses, medial and lateral, found 

 immediately dorsal to the ventro-lateral processes. The medial 

 mass is a quadrangular, inwardly concave plate, 28 mm. long, 

 whose long axis is parallel with the lower border of the meseth- 

 moid, with which its upper edge is in close apposition, being, 

 for the most part, only separated by perichondrium. It is much 

 the larger of the two, and lies at a lower level than the lateral 

 mass. The ventral extremity of the plate is drawn out to a 

 rather sharp free point, known as the ventral process (fig. 2), 

 its tip lying just below the septum. The lower border is marked, 

 rather nearer the ventral than the dorsal extremity, by a pro- 

 jection, directed downward, which, however, is terminated by a 

 sharp, backwardly turned point of cartilage, this structure 

 being known as the caudal process (figs. 2 and 18). The dorsal 

 termination is very blunt; it may be described as the dorsal bor- 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 16, NO. 4 



