The Arachnoid of the Brain.— In the N. Y. Medical Kte.nl. 

 Aug. 15, 1891, Dr. F. W. Langdon publishes some new observations 

 on the Arachnoid of the Brain which are summarized as follow*. 



"1. The arachnoid membrane is a true shut sac, similar in structure 

 and function to the serous membrane of the other great cavities. Its 

 parietal layer is easily separable from the dura at the vertex in the 

 foetus and young infant, but practically inseparable in this region in 

 the adults. At the base of the skull it is demonstrable as a separate 

 membrane even in the adult. To assert that the parietal layer of the 

 arachnoid is absent, because its subepithelial connective tissue has 

 fused at the vertex with the dura (connective tissue) is as incorrect as 

 to describe the great omentum as one layer of peritoneum, because its 

 original four layers have become matted and adherent." 



"2. The arachnoid cavity communicates freely with the subarach- 

 noid space, by means of two foramina situated in the visceral arach- 

 noid, one on either side of the medulla. For these I would propose 

 the name ' lunulate foramina,' from their crescentic or lunulated edges, 

 produced by the attachments of fibrous bands which cross the open- 

 ings transversely. Subsequent observations, in two instances, confirm 

 the presence of the 'lunulate foramina.' In one of these, the basilar 

 process of the occipital and the sphenoid body were cut away from the 

 base and the dura removed, so as to show the foramina in situ ; thus 

 excluding the possibility of their artificial production during the 

 extraction of the brain." 



