1890 - 91 .] Drs Symington & Thomson on Defective Ossification. 277 
skeleton, a brief reference may be made to the condition of the 
Brain. This organ was hardened in situ , and the entire head was 
then divided by a sagittal mesial section. Fig. 2 of Plate II. is a 
drawing of the right half of part of this section, while fig. 1 on the 
same plate shows the same structures in a normal nine months’ 
foetus. A comparison of these two figures will demonstrate the fact 
that the normal relations of the brain have been considerably 
altered, these alterations being secondary to those in the skull. 
The lower part of the medulla is notably diminished in size ; this 
is probably due to the smallness of the foramen magnum. The 
medulla and pons normally extend from the foramen magnum to the 
upper edge of the dorsum sellae, but in this case fully one-half of the 
pons lies above the level of the dorsum sellse. The long axis of the 
medulla and pons, which is usually directed from below upwards 
and somewhat forwards, is here inclined upwards and backwards. 
These changes w T ere obviously due to the decrease in the length 
of the base of the skull in front of the foramen magnum. The optic 
thalami are also displaced backwards and upwards, and lie between 
the splenium of the corpus callosum above and the corpora quadri- 
gemina below. Normally these two structures are only about *3 cm. 
apart, while in our case they are separated a distance of 1*3 cm. as 
measured from the splenium to the upper extremity of the nates. 
The posterior part of the corpus callosum is pushed upwards so that 
its antero-posterior arch is less marked than usual. The most strik- 
ing changes, however, we found in connection with the form and 
position of the cerebellum, which is flattened from above downwards 
and backwards, so that its long axis is directed from the foramen 
magnum upwards and backwards. Associated with this, there is an 
alteration in the attachment of the tentorium and in the situation of 
the lateral sinus, while the falx cerebelli is greatly increased in 
length. The torcular Herophili is 6*3 cm. distant from the posterior 
edge of the foramen magnum, whereas it is generally about 2*5 cm. 
The lateral sinus and attachment of the tentorium cerebelli correspond 
to the lambdoidal suture, so that the cerebellar fossa reaches to the 
upper limit of the supra-occipital. No distension of the third or 
fourth ventricles, the aqueduct of Sylvius or the foramen of Monro, 
is seen in the mesial section ; and after the removal of one-half of the 
brain and cutting into it, the lateral ventricle w r as also found of the 
VOL. XVIII. 1 / 8/91 2 A 
