400 CHAKLES CLIFFORD MACKLIN 



widest part of the septum. The outer edges of this border, except 

 in the upper portion of the crista galli, show short lateral emi- 

 nences, which project into the fenestra cribrosa. These projec- 

 tions will later coalesce with others from the upper edge of the 

 side-wall, and thus form the dorsal portion of the cribriform 

 plate. In front the crista galli passes over upon the cranio- 

 ventral border, which is straight, and sharply inclined downward, 

 while laterally it is directly continuous throughout with the ven- 

 tral portion of the tectum nasi. By reason of the fact that the 

 tectum rises somewhat, as it springs from the septum, the upper 

 border of the latter lies here at the bottom of a shallow furrow, 

 the sulcus supraseptalis (fig. 1), which reaches from the crista 

 to the ventral tip of the capsule. 



The ventral border of the septum is straight and free, and 

 marks the anterior extremity of the mesethmoid, forming the 

 medial limit of the incisura narina, the representative of the 

 fenestra narina of some of the lower forms. At its lower end 

 it meets the caudal border at an angle of 113°. The caudal 

 border is almost straight, horizontal, and thickened throughout, 

 but much more so dorsally than ventrally, so that it resembles a 

 cone, this similarity being rendered more striking by the fact 

 that the transition to the thin part of the septum above is quite 

 abrupt, thus resulting in the formation, on each side, of a shallow 

 furrow (figs. 14 to 18). Near the ventral extremity the caudal 

 border shows on the right side, but not on the left, a lateral con- 

 nection with the cartilages of Jacobson (fig. 11), and, in front 

 of this, bilateral unions with the ventro-lateral processes (Faw- 

 cett '11), the latter appearing immediately behind the front end. 

 Projecting backward from the posterior of these attachments, 

 lying parallel with and below the caudal border, in a position 

 corresponding to about the middle of its ventral half, may be 

 seen the cartilages of Jacobson, or the anterior paraseptal carti- 

 lages (figs. 2 and 18). Behind these the dorsal portion of the bor- 

 der, in its caudo-lateral aspect, is covered by the thin plates of 

 the vomer (fig. 2). 



The surfaces of the septum are for the most part smooth, but 

 in the region below the crista galli there is a deflection to the left; 



J 



