204 D. DAVIDSON BLACK 



Thus the conditions of these vessels may be looked upon as 

 being to some extent an indication of the degree of perfection 

 of cerebral growth. The two disturbances cannot be considered 

 as being mutually dependent upon one another, for the cerebral 

 condition in cases such as this is certainly the prime factor. 



There is a large blood supply from the median carotid to the 

 right half of the cerebral vesicle, while there is no component 

 to this side from the basilar artery. Oh the other hand, the left 

 side of the cerebral vesicle receives a large component from the 

 basilar artery which effectually compensates for the small supply 

 derived from the branches of the median carotid trunk on this 

 side. So, although the vessels are asymmetrically arranged, it 

 is to be noted that the blood supply is approximately equal on 

 •both sides. 



The sharp bend which is seen anteriorly in the median carotid 

 before it pierces the dura is similar to the bending of the normal 

 bilaterally symmetrical vessels before their division into anterior 

 and middle cerebral arteries. It is to be noted in this connection 

 that the single ophthalmic artery arises at this 'genu' as is also 

 the case with the normal ophthalmic arteries. 



Contents of the orbital fossa 



The following incomplete dissections were made by removing 

 the roof of the orbital fossa. Only those structures which could 

 be dissected without disturbing the external relations of the bul- 

 bus are described. The diagrams represent the structures in 

 this region as seen from above. All the structures examined 

 were essentially symmetrical. 



First stratum (fig. 8). On removing the bony roof of the 

 orbital fossa and dissecting away the peribulbar fat and connec- 

 tive tissue, the muscles of this region were found to radiate out- 

 wards to their insertions from a central fibrous mass in which 

 are imbedded the remnants of the unpaired optic nerve. 



In the region of the central tendon the third nerve divides into 

 a number of small branches and freely communicates with its 

 fellow of the opposite side. 



