IO2 



BIOLOGICAL PHYSICS 



buccal cavity takes place, and when a downward pitting 

 and eversion of the floor of the middle cerebral vesicle 

 shows itself ; this stage is followed by the extension 

 and approach towards each other of these diverticulations 

 or expansions, and by their final enclosure in a common 

 cyst wall, within which they afterwards maintain a separate 

 anatomical and histological existence, but co-operate in the 



performance of a common 

 function their textures, 

 the anterior and posterior 

 lobes respectively, being in- 

 dividually discernible, while 

 their functional work may 

 be regarded as common. 



The sella tunica^ or cen- 

 tral basi-sphenoid floor, 

 moreover, is the earliest 

 consolidated and ossified 

 texture of the human skull, 

 and, as such, maybe regarded 

 as of primary importance in 

 the support and accommo- 

 dation of the growing, as 

 well as the mature central 

 nervous system, so far at 

 least as concerns the brain 

 with its dependent pituitary 

 outlet. In association with 

 the formation of this solid 

 floor, as a foundation on 

 which the central great 

 nerve organisms comprised 

 within the cranial vault can be laid down, developed, or 

 built up in due order, we find that a series of at least 

 three, foramina, or openings, one central and two lateral, 

 is provided whereby the residual materials, resulting from 

 the progress of the great developmental processes then 

 being wrought out, can be removed, to prevent the 

 occurrence of encumbrances and contaminations. 



These foraminal exits (Figs. 33, 34, 35, 36) coincide in 

 number and position with the subjacent spongy, and, in 



FIG. 33. BRAIN AND SPINAL CHORD OF 

 A FOETUS OF FOUR MONTHS, SEEN 

 FROM BEHIND. (From Kolliker. ) 



//, hemispheres of the cerebrum ; >n, corpora 

 quadrigemina or mesencephalon ; c, cere- 

 bellum ; inn, medulla oblongata, the fourth 

 ventricle being overlapped by the cerebellum ; 

 .? J, the spinal cord with its brachial and 

 crural enlargements. 



