302 PRINCIPAL SIR W. TURNER ON 



sections of additional skulls are given with radial and other lines and measurements. 

 As suggested in my paper on Pithecanthropus erectus* an antero-posterior nasio- 

 tentorial plane, from the nasion to the upper border of the groove for the lateral sinuses,t 

 expressed the division of the cranial cavity into an upper cerebral part, occupying the 

 large space above the tentorium, orbital plates of the frontal, cribriform plate of the 

 ethmoid and great wing of the sphenoid ; and a basal part in which the cerebellum, pons, 

 and medulla are lodged. The division of the radial lines by the line nt, which indicates 

 the nasio-tentorial plane, marks off the upper cerebral part from the lower basal part, 

 and the diameter of the cavity where each radial line touches the inner table of the skull 

 is stated in Table VI. Further, a line drawn from the nasion to the bregma nbr, as has 

 been done by Professor Cunningham,! gives the chord of the arc of the frontal bone ; 

 the depth of the arc is measured by erecting a perpendicular from the chord to the 

 most projecting part of the frontal, whilst the depth of the cerebral space, which the 

 chord and arc enclose, is obtained by measuring the length of this perpendicular to the 

 point where it touches the inner table of the bone. The fronto-occipital diameter of 

 the cerebral cavity, and the diameter of the cavity from the perpendicular radius to 

 the frontal and occipital poles respectively, are given in Table VI. The lines inter- 

 secting the cranial cavity subdivide it into regions which indicate approximately the 

 position and relative magnitude of important divisions of the brain. The area of the 

 cerebrum below is defined generally by the nasio-tentorial plane. Though the plane of 

 the foramen magnum, from which the perpendicular radius is drawn at right angles, 

 varies in its inclination in different skulls, and is not necessarily parallel to the hori- 

 zontal plane of the head, the tentorio-perpendicular section of that radius has a, general 

 relation to the fissure of Rolando and to the posterior limit of the frontal lobe. The 

 space between the tentorio-perpendicular and tentorio-lambdal radii is associated with 

 the parietal and upper part of the temporal lobes, and the region behind the tentorio- 

 lambdal radius with the occipital lobe. The influence exercised by the frontal sinus on 

 the curvature of the inner and outer tables is shown in the figures reproducing the 

 sections, as well as the extent of the air sinus above the glabella. For purposes of 

 comparison Table VI. includes corresponding measurements of some of the skulls de- 

 scribed in Part II. of this series of memoirs, § details of which were not at that time 

 given, also measurements of sagittal sections of two skulls described in my memoir on 

 the Craniology of the People of Scotland. || 



* Journ. Anat. Ph/ys., vol. xxix. p. 424, 1895. 



t The inion on the outer table is, as a rule, lower down than the upper border of the groove for the lateral sinus 

 on the inner table which marks the attachment of the tentorium, hence the term nasio-tentorial plane is to be pre- 

 ferred to nasio-inial plane. 



I " The Brain of the Microcephalic Idiot," Scientific Transactions of the Royal Dublin Society, vol. v. p. 344, fig. 16, 

 1895. 



§ The Veddah, Gond, Munda, Bhumij, and Pan Cole skulls are described and measured in Part ii., Tables i., 

 iii., iv., ix., Trans. Roy. Soc. Edin., vol. xl., 1901. 



|| Trans. Roy. Soc. Edin., Tables iii., xiii., xvii., 1903. 



