156 THE DEVELOPMENT OF THE CHICK 
ment of the nuclei leaves thin non-nucleated strips (septa) be- 
tween adjacent neuromeres. The interneuromeric projections are 
most pronounced laterally and fade out dorsally and ventrally. 
Behind the neuromeric portion of the hind-brain is a portion 
extending to the posterior end of the fourth mesoblastic somite 
from which the twelfth cranial nerve arises. 
The Neural Crest and the Cranial and Spinal Ganglia. The 
cranial and spinal ganglia owe their origin to a structure known 
as the neural crest, which is a practically continuous cord of cells, 
lying on each side in the angle between the neural tube and 
the ectoderm, extending from the extreme anterior to the pos- 
terior end. Like other meristic structures the anterior portion 
Vy 
Am V4 VL. 
t 
Chor __ 
1 
| 
t 
Wil MONS yg Gr ae 
YS. 
Fic. 89. — Frontal section of the hind-brain region of an embryo of about 
36s. 
Ot., Otocyst... N.°6, N.. 7,..N. 8, .N, 9, Ne 10; N. 11, Neuromeres, 6 to 11, 
according to Hill’s enumeration. s. 1, s. 2, s. 3, First, Second, and third 
somites. V, Primordium of the trigeminus. VII-VIII, Primordium of the 
acustico-facialis. 
of the neural crest is the first to arise (at about 6—-7s stage), 
and the remainder appears in successive order during or shortly 
after the closure of the neural tube in each region; thus it is not 
until after the completion of the neural tube that the last portion 
of the neural crest is established. 
But before this time successive enlargements of the cranial 
part of the crest have formed the primordia of the cerebral gan- 
elia, and similar successively arising enlargements of the parts 
of the crest opposite the mesoblastic somites form the rudiments 
of the spinal ganglia. The intervening portions of the crest form 
the so-called interganglionic commissures, which subsequently 
