388 CHARLES CLIFFORD MACKLIN 



and project upward, outward and forward in a horn-like manner, 

 so that their ventral extremities overlie, to some extent, the 

 hypophyseal fossa. These are the posterior clinoid processes. 

 Their upper extremities rise higher than the cranial edge of the 

 dorsum sellae between them, and hence the latter is concave 

 cranially, as well as ventrally. The dorsal surface of the dorsum 

 sellae is gently concave from side to side, and from above down- 

 ward, passing uniformly over upon the surface of the otic por- 

 tion of the planum basale below. 



Histologically there is here, at this stage, no evidence of the 

 primary separation of the chondrous anlagen of the dorsum 

 sellae, such as Fawcett describes in earlier stages (19 and 21 mm.), 

 except a slightly younger condition of the cartilage at the ventral 

 side of the junction of the dorsum sellae and crista transversa. 



In front of the dorsum sellae we come upon the wide, flattened 

 floor of the hypophyseal fossa (fig. 1), or sella turcica, which 

 opens laterally into the side-parts of the middle cranial fossa, 

 and is thus more correctly a short wide groove than a fossa. 

 Ventrally the wall rises abruptly, — almost vertically, — to reach 

 a transverse ridge, — the anlage of the tuberculum sellae. The 

 lateral edge of the ventral wall presents, on the right side, but 

 not on the left, a small, conical backwardly projecting middle 

 clinoid process. The tuberculum sellae of my model is much 

 more prominent than it is in that of Hertwig. It is interesting 

 to note in passing that Levi is of the opinion that in the develop- 

 ment of the human skull the sella turcica is the only part to 

 retain its primitive position, the other parts moving cranially, 

 and he finds in the 28 mm. stage, among other evidences of 

 this, the appearance of the tuberculum sellae as the anterior 

 wall of the sella turcica. There is no evidence of the tuberculum 

 sellae in the 17 mm. stage, while in the 28 mm. stage the sella 

 has a vertical ventral wall, as in my model. 



The part of the central stem of the chondrocranium compos- 

 ing the floor and ventral wall of the sella turcica has been termed 

 the Balkenplatte or lamina trabeculi. It is wide, and, when 

 compared with the parts in front and behind it, quite thin. It 

 shows no evidence of perforation. From the ventral half of each 



