mi. .1 i in: .. liM 



more oblique, and tinally, in the him'' so in 



the sacral, it is moiv .sharply downward. On tin- account the i 



ariHiiu' from tin- la-4 part of the .-pinal eord come to lie for a 

 con-id, rable distance in the \vitel.ral eanal before they reach the 

 -acral foramina serving for their exit ; they tli.-i. : ound tho 



conus medullaris ami lilnm terminal.', forming the >trueture known 

 as the hoieo-f ail or eauda t <piina. 



Finally the .-.pinal cord underlie.- >omo changes in i'- form 

 Kvcn in tliothinl and fourth months tin -re aj^.t-ar liH-i-i-ncrs of i-alil in- 

 indifferent regions. The places in the ccr\ical and luml-a 

 of the spinal cord at which the i.eri[.hrral ncrv< bo the ant.-i ior 



and posterior extremities, ^row vigorously hy tlu- ahundant formation 

 of ganglionic cells ; they become con>idrral>ly thicker than the adjoin 

 inir portions of the cord, on account of which they are di-tiniruiMied 

 as cervical and luinliar <iilargementa (int umocentia cervicalis et 

 hnnbalis), 



(b) The Development of the Br 



By the study of embryology knowledge of the anatomy of the 

 brain has been greatly promoted. Justly, therefore, in all recent 

 text books of human anatomy, the embryonic condition serves as 

 the starting-point in the description of the intricate structure of the 

 brain, the aim being to derive thn complicated ultimate conditions 

 from the more simple embryonic ones, and to explain them by means 

 of the latter. 



The initial form of the brain as well as of the spinal cord is a simple 

 tube. At an early period, even before it is e\. i \ where clase 

 becomes metameric, on account of its growth being greater in some 

 regions than in others. By means of two coiiMrictions ,.f its lateral 

 walls it is divided into the three priin<n- ; i \\. S7 hb l ,hb 2 , 



M 3 ), which remain united with one another by means of wide openings, 

 and are designated as the fore-, mid-, and hind-brain. The posterior 

 of these divi>ions is the lon_;t-i. gradually taperinir and l>ecoming 

 continuous with the tubular >pinal cord. 



The lii>t Stage is quickly followed by a second, and that by a / 

 since the primary bra in-\c.-icles >oon -eparate into four, and linally 

 five divi.M- 



During the second stage (fig. 23-t) the lateral walls of the primary 

 fore- brain (pi'h) begin to grow outward more vigorously and to 

 evaginate to form the two optic vesicles (cm). At the same time the 



