EXTRACT XLIX.A. 



ON THE OSSEOUS COVERINGS OF THE CENTRAL 

 NERVOUS SYSTEM. 



A SYSTEM of the importance to the vital well-being of 

 the individual organism, such as the systemic nervous 

 system undoubtedly is, would seem to require for its 

 accommodation, support, and protection, a hollow osseous 

 structure, stable enough to afford a material foundation 

 on which it can rest, and yielding enough to permit of 

 a certain measure of movement of its component parts 

 to meet the requirements of the remainder of the 

 osseous skeleton, to which it is articulated in relation 

 to position, locomotion, and prehension. This hollow 

 osseous structure is provided in the skull and spinal 

 column, and is developed, by a process of ossification, 

 from a series of central points laid down in the 

 embryonic matrix surrounding the nascent central nerve 

 elements. 



That part of the bony structure of the body here 

 referred to is the earliest to be laid down of the skeletal 

 framework, in and around which the soft structures com- 

 posing that body can grow, or are developed, with safety 

 and regularity in obedience to the laws of development 

 and evolution. The structure of the bones of the skull 

 is a compound of originally separated cartilaginous or 

 membranous and independent osseous units, but finally 

 of a closely articulated and continuous osseous enclosing 

 envelope, and consists of an outer and inner more or less 

 solid framework, with a central spongy or porous diploe ; 

 this latter, in the case of the skull bones, terminating in, 



