MEGALONYX LEIDYI, JST. SP. 5 



distance, a little behind the middle of the canal, the septum in the canal of the left 

 side is complete through its entire length, and is 6 mm, thick in the centre of its 

 anterior border. The anterior orifices are vertically oval, that of the right side meas- 

 uring 13.5 X 9 mm. ; the upper orifice on the left side measuring 8x5 ram., and the 

 lower, 11 X 9 mm. 



Resting on the zygomatic process of the maxilla, the root of the malar hone pro- 

 jects outward, backward, and downward, its antero-posterior diameter being 12 mm., 

 the intero-exterior 21.5 mm. in its narrowest place, about 12 mm. below the summit 

 of the curve of the said process. About 9 mm. further down, on the interior side, is a 

 tuberosity forming the superior termination of an area for muscular attachment. 

 This area, 10 mm. wide and 41 mm. long, twists itself around the border of the bone, 

 so that its lower end faces directly forward. It is divided by a low, median longi- 

 tudinal ridge into two facets. 



From the border, beaiing this area, the external surface of the bone turns out- 

 ward and backward, and at the same time expands both upward and downward ; 

 the anterior border of the upper expansion forms the exterior border of the orbit, and 

 terminates about 5 cm. above the inferior orbital border in a postorbital protuberance; 

 whilst the downward expansion is j)rolonged into a free descending rarmis, terminat- 

 ing abruptly, 9G mm. below the inferior border of the orbit. A low ridge passes 

 from the infero-posterior corner of this ramus, on its exterior face, diagonally upward 

 and forward, dividing that face into two concave facets, of which the antero-inferior 

 is triangulfir in form, the other somewhat rhomboidal. The inferior as well as the 

 posterior borders of the ramus are attenuated to sharp edges ; its anterior face is 

 triangular, and by a sharp ridge set off from the exterior face ; its interior face is 

 smooth and convex. 



Posterior to a line, which may be drawn from the postorbital protuberance of the 

 malar bone to the posterior margin of the descending ramus, the exterior face of the 

 bone bends more strongly backward, and the corresponding line on the interior face 

 is the anterior marsfin of the broad shallow fossa which extends to the semicircular 

 ridge near the distal end of the zygomatic process of the squamosal. The free pos- 

 tero-inferior margin of this laminar body forms a sharp edge, and, on the external 

 face, bordering on this edge, is seen a semicordate muscular impression, pointed 

 behind, oval in front, and reaching nearly half way towards the inferior margin of 

 the orbit. 



A line drawn from the postorbital protuberance of the malar to the nearest point 

 of the zygomatic process of the squamosal, may be regarded as the base of the ascend- 

 ing ramus of the latter. Below this line the external face of the bone slopes down- 



