P.Co/- 



THE PINEAL ORGAN OF MAMMALS 



307 



P.O. 

 M-C.H. 



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«:"■ \ 



l£M. 



■7.i?fl. 



C.Ep. 

 (S.C.O.) 



B 



Fig. 213. 



A — Transverse section through the pineal organ of a human embryo (6 cm.) 

 showing its relations to the membranes, posterior commissure, and sub- 

 commissural organ. 



B — A median linear reconstruction of the pineal region of a human embryo 

 (6 cm.) showing the main diverticulum, infrapineal recess, anterior lobe, 

 superior and posterior commissures, the dorsal sac, and an anterior diverti- 

 culum possibly representing a vestige of the paraphysis ; also the great 

 cerebral vein and opening of the aqueductus cerebri. (R. J. G.) 



A.L. : anterior lobe. 

 Aq. C. : aqueductus cerebri. 

 C. Ep. : columnar epithelium 

 C.H. : cerebral hemisphere. 

 D.D. : dorsal diverticulum 



pineal recess. 

 G.C.V. : great cerebral vein. 

 I.P.R. : infrapineal recess. 

 Pa. : ? paraphysis. 

 P. Co. : posterior commissure 



P.D. : pineal diverticulum. 

 P.M. : pia mater. 

 P.O. : pineal organ. 

 Post. D. : posterior diverticulum, 

 or supra- P. St. : pineal stalk. 



Q.P. : quadrigeminal plate. 

 S.C. : superior commissure. 

 S.C.O. : subcommissural organ. 

 I 7 . III. : third ventricle. 



In a 22-mm. human embryo, Figs. 212, A, B, C, D, the simple primary 

 diverticulum is subdivided by a transverse fold into a hollow, bilobed 

 anterior segment, B, A.B.D., and a single median posterior segment, 

 B, P.M.D. The superior or habenular commissure has also appeared 

 and two diverticula from the dorsal sac have commenced to grow back- 



