48 PROFESSOR OWEN ON THE AYE-AYE. 



little in advance above, where the suture shows slight crenulations, and gets behind 

 the ridge before it passes down between the mastoid and superoccipital. 



The interparietal (ib. fig. 1 , 3) is a small triangular bone, without trace of sagittal suture, 

 10 lines in length, and the same across the base, which is posterior, forming the middle part 

 of the lambdoidal suture. The outer surface of the interparietal is divided into three 

 nearly equal longitudinal tracts by the back part of the temporal ridges. The exposed 

 inferior surface of the basisphenoid is rather shorter and broader than the basioccipital, 

 but it is prolonged further along the cranial floor, where it is expanded by a large sinus 

 (i6. fig. 6), and coalesces with the presphenoid. The alisphenoid developes the ectoptery- 

 goid ridge, extending from between the squamosal and tympanic to the outer side of the 

 entopterygoid ; both plates are imperforate. Above the back part of this ridge is the 

 foramen ovale (ib. figs. 2 & 5,/), three lines in advance of which is the foramen rotundum. 

 The natiform protuberances form deep depressions in the alisphenoid, on each side the flat 

 square platform of the cranial surface of the basisphenoid, in the middle of which is the 

 subcircular pituitary pit (ib. fig. 5, k). There are no clinoid processes. The alisphenoids 

 join the parietals, which contribute the greatest share to the formation of the calvarium. 

 The tympanic (ib. fig. 2, as), coalescing with the petrosal, is, together with that element, 

 expanded into an oval bulla (ib. x) on each side of the basisphenoid. The sagittal suture 

 is almost a harmonia, 11 lines in length. The temporal ridges extend each to within 

 1^ line of the hind part of the sagittal suture, but diverge as they pass to the postorbitals. 

 The parietals, impressed from within to transparent thinness by the longitudinal convo- 

 lutions of the cerebrum, do not exceed half a line in thickness elsewhere. Between the 

 root of the zygoma and the lambdoid ridge there extends a ridge at right angles to the 

 latter. 



The coronal suture crosses the cranium transversely three lines behind the post- 

 orbitals : the frontal suture remains ; its length is 1 inch 5 lines ; like the sagittal, it is a 

 harmonia. The fore part of the frontals (PI. XX. fig. 1, n) projects a httle between the 

 origin of the nasals (ib. i^), and also between the nasals and maxillaries ; they then join 

 the lacrymals, form the upper half of the inner wall of the orbit, and unite behind with 

 the orbitosphenoid, alisphenoid, and parietal. The postorbital process is three-sided, 

 almost 5 lines in length, contracting to its junction with the malar (ib. 26) : there is a 

 slight depression at its base, defining the superorbital ridge. This ridge is entire, 

 neither perforated nor notched. The olfactory fossa, within the cranium (ib. fig. 5), 

 is subcircular, 7| Unes in breadth, and 6 hues in length. The median septum is 

 produced with a ' crista galli.' The frontal sinuses (ib.j) give no outward indication, 

 but are large and extensive, about 3 lines at their widest part from front to back 

 wall, extending 1 inch 4 lines transversely into the bases of the postorbitals, and 

 backward to within 5 lines of the coronal suture ; they are divided from each other 

 by a median bony septum ; each division communicates with the nasal chamber by 

 a median orifice, and by a lateral one with the antrum. The nasals (PI. XIX. is) 



