294 MAMMALIAN ANATOMY 



Usually two scrolls are placed between two partitions ; below the 

 lowest partition is a single more swollen scroll. The scrolls also are 

 attached by their posterior ends to the cribriform plate. The broad 

 posterior border of the cleft already described namely, the border 

 from which the edges of these partitions appear to arise presents an 

 upper third which is flat and square, faces upward and outward, 

 and together with the anterior end of the first partition is more or less 

 closely united with the upper part of the inner surface of the nasal 

 process of the maxillary bone. At the upper anterior edge of this 

 border is attached the upper outer end of a broad curved plate which 

 extends downward and backward as the greater part of the anterior 

 wall of the dividing cleft, forming a posterior shield to the small scrolls 

 which make up the anterior triangular part of the bone. As we shall 

 see, this cleft plate is a downward leaf of the curved plate which covers 

 the top of these small scrolls. This plate in turn is part of the third 

 scroll seen in the inner or medial surface of the lateral ethmoid (Fig. 

 219, m). The plane of the lower two-thirds of the plate-like posterior 

 border of the cleft forms an angle with the plane of the upper third, 

 facing outward and backward ; at about its middle, between the anterior 

 ends of the third and fifth partitions, is a wider portion which is flat 

 and elevated and applied to the anterior part of the inner surface of 

 the orbital plate of the frontal. A part of this area, usually a round 

 or oval patch, is smooth and dense, and often appears on the inner 

 wall of the orbit between the frontal, the lachrymal, and the palatine 

 bone, as the os planum (Fig. 211). The rest of this strip, bounding 

 the cleft behind, is depressed and concave ; it is overhung above and 

 behind by the elevated portion, and does not touch the investing 

 lachrymal bone, nor is its lower edge in contact with the inner surface 

 of the vertical plate of the palatine bone. The partitions lying between 

 the scrolls are attached to corresponding ridges on the inner surface of 

 the frontal, except the anterior ends of the first and second, which 

 join the maxillary, and the lower ends of the sixth and seventh parti- 

 tions, which with the lower border are applied to the palatine (Fig. 

 214). 



The upper part of the seventh partition is attached to the inner 

 wall of the sinus in the presphenoid, which contains the lowest scroll 

 (Fig. 213). 



The attachment of these partitions to the plate in which they ter- 



