CRANIOMETET AND CEANIO GRAPH Y. 353 



estimated, according to the metliod proposed by Eetzius, who mea- 

 sured the distance from the external auditory foramen to the gla- 

 bella, and to the most projecting part of the occiput. 



10. The external auditory foramen is, relatively speaking, a fixed 

 point, as has been pointed out by Carus. But, at the same time, 

 its position must not be regarded as absolutely fixed. At any rate, 

 its position with respect to the foramen magnum is liable to vary. 

 Oenerally speaking, a transverse line drawn through the centre of 

 each opening, would pass over the anterior part of the foramen mag- 

 num, and consequently would nearly correspond with the line of 

 support — but sometimes it will run a little in front of this direction, or 

 over the anterior margin of the foramen, or even in very short skulls 

 altogether in front of it. A circumstance which should be noted. 



11. Besides the extreme breadth Prof. v. Baer takes three latitu- 

 dinal measures at different poiuts, viz. : at the forehead, the parietal 

 eminences, and behind the ear, that is to say at the junction of the 

 parietal and occipital regions. 



The frontal region is measured first at the narrowest part in front 

 or immediately behind the external orbital process — (not including 

 the temporal ridge) and secondly, towards its posterior part, or close 

 upon the coronal suture, the greatest width at this part being just 

 below the temporal ridge. 



12. The distance between the centres of the parietal protuber- 

 ances. 



13. 14. In order to determine the development of the hinder 

 part of the cranium where the occipital region begins, he takes a 

 point on a horizontal level with the auditory opening and in a 

 straight line behind it, and iaimediately behind the border of the 

 base of the mastoid process, and measm-es the distance between the 

 corresponding points on either side. This line may be regarded as 

 the chord of the arc measured from the same points over the vertex. 

 The value of the points above indicated is not so arbitrary as it 

 might seem, since it corresponds to the curve of the transverse 

 sinus, and the chord gives an approximate measure of the breadth of 

 the tentorium and of the space for the cerebellum. AU these 

 measures do not give absolutely the dimensions of the cerebral 

 cavity, but they are comparable inter se, and except the glabella the 

 points from which they are taken are so selected as to approach near 

 the cavity. 



15. In order to estimate the space occupied by the braiu, the 

 skull must be sawn in two — which is best done in the medial plane. 

 The length of the bodies of the cranial vertebras, he says, (not quite 

 truly) can now be measured by a line drawn from the anterior angle 

 of the foramen magnum to the foramen coecum. The length of the 

 arc from the latter point to the foramen magnum is also displayed • 

 whilst at the same time the angle formed between the upper surface 

 of the basilar process with the plane of the foramen magnum, and 

 with the cribriform plate of the ethmoid is clearly seen. The alti- 



