THE PINEAL ORGAN OF MAMMALS 315 



There is thus an appearance produced, by cross-sections of the cords, 

 of groups of deeply stained epithelial cells arranged in ring-like zones 

 or " rosettes." These surround the vascular ingrowths, which appear 

 pale. This arrangement of alternating series of branched epithelial and 

 vascular cords is the key to the mosaic appearance which is described by 

 Globus and Silbert as characteristic of the later stages of foetal and early 

 postnatal life. The " streams" of deeply stained epithelial cells described 

 by these authors are longitudinal sections of the epithelial cords. The 

 central parts of the large clear areas of the mosaic pattern are transverse 

 or oblique sections through the ingrowing vascular processes surrounded 

 by pale cells with vesicular nuclei. Owing to the radial disposition of the 

 epithelial cells around a central axis, which is destitute of nuclei, the 

 general appearance of a group of epithelial cords cut transversely is similar 

 to that of an acinar gland, but with the important difference that in 

 the human subject the acini usually have no lumen and no ducts are 

 present. 



The later foetal and early post-natal stages of development of the 

 human pineal organ have been specially studied by Globus and Silbert, 

 1 93 1, and Krabbe, 1915 ; the former have published an excellent series 

 of photographs of the pineal body, illustrating the structure of the organ 



the lumen of the diverticulum into the outgrowing processes is much more 

 pronounced. Below and to the right of the photograph are seen sections of 

 portions of the paraphysis and dorsal sac. 



C — Transverse section through the basal part of the pineal evagination of the 

 4i-month human foetus, seen in Fig. 214, B, C, and D, showing outgrowth 

 of neuro-epithelial cords, more especially from the anterior aspect and sides 

 of the tube ; on the posterior aspect (below in photograph) the epithelium 

 is differentiating into the columnar type characteristic of the subcommissural 

 organ. 



D — Detail of B, ■ 139 D., showing in the centre a pseudo-lobule, with its central 

 core of vascular pia mater, between two hollow neuro-epithelial outgrowths. 



E — Section through the subcapsular part of a pineal gland of an infant (1 year 

 4 months), showing the fibrous capsule and the penetration of a blood-vessel 

 inro the substance of the gland. The vessel is surrounded by a perivascular 

 sheath of fibrous connective tissue, outside which is a glial sheath the cellular 

 and fibrous components of which are continuous with the neuro-spongium 

 which forms the supporting tissue of the lobules and contains the parenchyma 

 cells. 



F — Portion of the same specimen 261 D., showing the predominance at this 

 stage of the cells with small dark nuclei and the arrangement of the cells in 

 cords, which when cut in cross-section are seen to be disposed radially round 

 a central core which is destitute of nuclei, giving the acinar appearance some- 

 times described as " rosettes." (R. J. G.) 



B.V. : blood-vessel. M.Z. : marginal zone. 



C.E. : columnar epithelium. P. Sh. : pial sheath. 



E.L.M. : external limiting membrane. Pr. Ep. : epithelial processes. 



Ep. : ependyma. Ros. : " rosette." 



F.C. : vessels in fibrous capsule. S.E. : secondary evagination. 



G. Sh. : glial sheath. V.C.T. : vascular connective tissue. 



