[178] 



Zbc Development of tbe tTabpoIe^ 



By J. W. Gatehouse, F.I.C. 

 Part VII. Plates XVII. and XVIII. 



THE development of brain and muscle, the organs of the will 

 and sensation, and the moto-mechanisra whereby the will 

 places itself in relation to external objects, is the subject 

 of the present paper. 



Brain and muscle are as necessary to each other as is the boiler 

 to the piston of the steam-engine ; without fire and boiler to 

 generate steam, the piston could not move, and without the brain 

 or similar exciting agency muscle would remain quiescent although 

 possessed of the inherent property of contractility. In the boiler 

 we know that water is by heat changed into a gas occupying some 

 two thousand times the bulk of the original liquid, and it is by 

 the pressure thus generated that the moving mechanism is set in 

 motion. 



Where in the brain shall we find the analogue of this? 

 Whence does the will originate? What is the nature of the 

 force transmitted from the brain through the nerves to the 

 muscles ? We know that certain nerves are capable of being 

 affected by definite sensations and by no others; but what causes 

 the difference in the capabilities of various nerves appears to be 

 totally unknown to us in the present state of our knowledge. 



These psychological questions, though most interesting, cannot 

 be answered, and even if they could be, do not fall within the 

 scope of these papers, which treat of purely physiological 

 conditions, and deal only with the visible changes undergone by 

 any organ from its commencement to the period of full develop- 

 ment. In the diagrams accompanying the former papers on this 

 subject will be found numerous stages of the development of the 

 brain and spinal cord, special reference being directed to Plate II., 

 Figs. I, 2, and lo of Part I.; Figs. 4 and 5, Plate VII.; and 

 Figs. 2, 3, and 4, Plate VIII., Part II.; Figs. 2 and 3, Plate XIII., 

 Part III.; Fig. i, Plate XX., and Fig. i, Plate XXL, Part IV.; 

 and Figs, i and 3, Plate XL, Part VI. : which taken together give 



