THE SPINAL CORD AND BRAIN. 



75 



TABLE OF BRAIN DEVELOPMENT. 



Telencephalon 



i. Fore-brain 



(Lateral and third ventricles) 

 Kl 



2. Mid-brain 



(Iter) 



Diencephalon 



Mesencephalon 



Optic vesicles. 

 Hemispheres. 

 Olfactory bulb. 

 Corpus striatum. 

 Lamina terminalis. 

 Infundibular gland. 



Epiphysis. 

 Thalamus. 

 Tuber cinereum. 

 Pars mammilaris. 



Corpora quadrigemina. 

 Cerebral peduncles. 



3. Hind-brain 



(Fourth ventricle) 



Isthmus. 



Cerebellum. 



Pons. 



Metencephalon 



Myelencephalon Medulla oblongata. 



R.d. 



Can. 



The spinal cord develops in an essentially uniform manner except at its caudal 

 extremity, the development of which is Part. G. B. D.H. 



arrested before differentiation sets in. 

 The undifferentiated extremity becomes 

 the filum terminale of the adult. Typi- 

 cally, the three primary layers, ectoglia, 

 cinerea, and ependyma, are early differ- 

 entiated. The ectoglia increases in thick- 

 ness and receives many nerve-fibers, 

 which run for the most part lengthwise, 

 and is thus transformed into the white 

 matter of the adult cord. The cinerea 

 becomes the gray matter and gradually 

 assumes the characteristic adult outline in 

 cross-sections (dorsal and ventral horns). 

 The ependymal layer remains thin, its 

 cells contributing to the formation of the 

 neuroglia frame-work. During the growth 

 of the cord, the ventral zones enlarge 

 rapidly and each projects downward, 

 leaving a notch between them (compare 

 Fig. 213, Sp.c). The notch is closed on 

 its dorsal side by the thin floor-plate by which the two ventral zones are con- 

 nected across. The ventral expansions increase and the notch is thus trans- 



Fiss. 



V.H. 



FIG. 40. TRANSVERSE SECTION OF SPINAL CORD OF A 

 HUMAN EMBRYO OF 32 MM. 



B, Burdach's column. Can, Central canal. D.H, 

 Dorsal horn. Fiss, Ventral fissure. G, Goll's 

 column. Part, Dorsal partition. R.d, Dorsal 

 nerve root. V.H, Ventral horn. 



