THE PINEAL BODY 



77 



The primary arches consist of the paraphyseal arch, the post velar 

 arch, the epiphyseal arch and the pars intercalaris (synencephalic arch) 

 and together with the velum are formed in the roof of the forebrain of 

 early sheep embryos. 



The paraphysis can be followed in practically all sheep embryos 

 from 20 mm. up to 48 mm. It is characterized by its short, broad, and 

 irregular outline and its solid structure, the cavity being in most cases 

 reduced to a minimum. 



P.V.A. 



Fig. 43 Reconstruction showing development of the pineal region in man. 23 

 mm. embryo, according to John Warren, 1917. 



L.T., lamina terminalis; P., paraphysis; V., velum; P.V.A. , Post-velar arch; 

 E., epiphysis; P.C., posterior commissure. 



