CHAPTER 17 



THE PINEAL SYSTEM OF VERTEBRATES 



THE PARIETAL REGION 



Before commencing the description of the pineal system of verte- 

 brates, it will be necessary to define certain terms which are applied 

 to structures included in the parietal region of the brain, namely, that 

 part of the roof of the interbrain or thalamencephalon which lies be- 

 tween the paraphysis in front and the posterior commissure of the 

 midbrain or mesencephalon behind. These structures are seen in their 

 A C Ec. 



- E P- ,Ec. Ep.^ 



VB! 



Fig. 130. — Sagittal Sections of Acanthias Embryos, showing Structures 



in the Roof of the Diencephalon. (After C. S. Minot.) 



A : 15 mm. embryo ; B : 28 mm. embryo ; C : 70 mm. embryo. 



A 1 : Plane of section, Fig. 139, A. 



B 1 : Plane of section, Fig. 139, B. 



ds. : dorsal sac. hg. : habenular ganglion. 



Ec. : Ectoderm. p. : paraphysal arch. 



Ep. : Epiphysis. MB. : midbrain. 



FB. : forebrain. pc. : posterior commissure. 



he. : habenular commissure. p. int. : pars intercalaris. 



V. : velum transversum. 



simplest form in the embryos of certain Teleostean fishes, e.g. Acanthias 

 vulgaris (Fig. 130), or among reptiles, Lacerta muralis (Fig. 173, Chap. 20, 

 p. 244). 



From before backwards these parts include : 



(1) The paraphysis. 



(2) The velum transversum. 



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