66 BIOLOGICAL PHYSICS 



infundibulum, the pituitary gland, with which it is encap- 

 suled, and the mucosa of the buccal cavity, which was 

 embryonically projected upwards to, and indissolubly 

 united with, the cerebral downward projection of the floor 

 of the third ventricle. 



A free posterior drainage is effected through the foramen 

 magnum into the cerebro-spinal cavity externally, and the 

 central canal of the cord internally, through which the 

 residuary products of the cerebral waste and overplus fluid 

 are allowed to gravitate, or be driven along the lines of least 

 resistance. 



The whole spaces and inter-spaces of the brain and its 

 overlying meninges, being continuous with each other, 

 allow the passage of cerebro-spinal fluid to circulate in 

 every direction within, and without, the brain, and to 

 obtain, whenever necessary, a free but guarded exit 

 the Pacchionian bodies providing a series of safety 

 valves, especially along the roof of the skull, where 

 drainage is not otherwise provided for. 



The posterior extremity of the cerebro-spinal canal is, 

 in our opinion, provided with a somewhat elaborate, but 

 intrinsically most ideally perfect, system of drainage, 

 effected by embryonic metamorphosis during the develop- 

 mental division and differentiation of the neurenteric 

 canal, the lumen of the canal being reduced to the 

 dimensions of the filum terminals of the cord, which 

 remains porous to the passage of cerebro-spinal fluid, and 

 the coccygeal gland, which acts as a cystic receptacle, or 

 lymph heart, provided with a series of " modified sweat 

 glands " encircling more especially the postero-lateral 

 aspect of the anus, and of ductiform outlets within the 

 anus. 



Besides these particular exits for superabundant and 

 effete cerebro-spinal fluid, a great general system of 

 excretion, or drainage, is provided through the sweat 

 glands situated more or less plentifully over the entire 

 surface of the skin, and acting individually and collectively 

 accordingly as the necessity for the action is local, or 

 general, the fluid reaching these glands along the inter- 

 neurilemmar spaces of the nerve trunks, fibres, and fibrils, 

 where the <c terminal " fibrils which reach the glands pour 



