224 



BIOLOGICAL PHYSICS 



taking place simultaneously, and, so, maintaining a per- 

 sistent, continued, but modified continuity, of the two 

 divisions of the canal. 



After this simultaneous separation and reunion of the 

 canal, its anterior limb becomes the alimentary, while its 

 posterior limb becomes the neural, canal, each of which 

 canals continues to perform the functions of a canal, and 

 to keep up a modified connection with each other, in the 

 performance of their respective, but absolutely different, 

 functional (Fig. 87) roles. 



B 



FIG. 86. OUTLINES SHOWING THE RELATION OF THE AXIS OF THE 

 EMBRYO TO THE OVUM IN BIRDS AND MAMMALS. (A. T. ) 



A, Fowl's egg opened after 35 hours' incubation, showing the embryo chick within the 

 transparent and vascular area on the surface of the yolk ; at right angles to the 

 long axis of the egg ; B & C, two early stages of development in the ovum of 

 the dog, showing the primitive streak (in B) and the commencing embryo (in C) ; 

 the line of the uterine tube and long diameter of the ovum being at right angles 

 to the vertebral axis of the embryo. 



The alimentary canal remains an open canal, secured at 

 its extremities by mechanisms of entrance and exit, to 

 provide for the reception, retention and residuum dis- 

 posal, of the alimentary materials supplied to the body ; 

 while the neural canal, receives into its own central cavity, 

 along with the intra-spaces of its peripheral tributaries the 

 systemic nervous system comprised of, brain, cord and 

 nerves, providing a great fluid surrounding and inter- 

 penetrating space, in which all these neural elements can 

 float, secured, and insulated, from centre to periphery, 

 and from periphery to centre. 



The alimentary canal is provided with a series of locks, 



