II. THE SKUT L OF A HmiAN FETUS OF 40 MM.» 



CHARLES CLIFFORD MACKLIN 



James H. Richardson Fellow in Anatomy, University of Toronto 



Regio orbitotemporalis 



The orbitotemporal region, in the present stage, is composed 

 of the cartilage of the sphenoidal anlage and unites the otic 

 region, behind, with the ethmoidal region in front. In it we 

 recognize an unpaired, median portion, made up of that part 

 of the central stem of the chondrocranium which contains the 

 bend; this represents principally the cartilaginous body of the 

 sphenoid, and is directly continuous dorsally with the otic portion 

 of the planum basale and ventrally with the nasal septum of 

 the ethmoidal region. In addition there are two paired, lateral 

 parts, the forerunners of the greater and lesser wings. The 

 internal pterygoid plate, which is laid down in membrane bone, 

 will be considered in the section devoted to the discussion of the 

 purely osseous elements. 



If we examine, successively, the parts of the median portion, 

 beginning dorsally, we note first a prominent transverse ridge, 

 the crista transversa (fig. 5), which marks the boundary between 

 the orbitotemporal and otic portions of the median stem. Di- 

 rectly continuous with this ridge, and springing upward from it, 

 is the prominent dorsum sellae (figs. 1 and 3), here showing no 

 median perforation, as it does in the rabbit (Voit), and it is 

 owing to this circumstance that the upper edge of the crista is, 

 in homo, entirely obliterated. 



The dorsum sellae forms the conspicuous posterior wall of the 

 hypophyseal fossa. Its upper and lateral corners are thickened 



1 Part I of this paper was published in the July numbor of the .Journal, vol. 

 16, no. 3. 



387 



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

 SKPrEMHEH, lull 



