. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 724 Biology of the Vertebrates this region remains relatively thin there are large optic ventricles which are not separated from the aqueduct. The infundibular region and the thalamus proper are small. The epi- thalamus includes a pair of habenular ganglia connected by a commissure as in all vertebrates. There are two outgrowths from the habenular region: a well developed epiphysis {pineal organ), anterior to which is a smaller parietal body. These two org
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 724 Biology of the Vertebrates this region remains relatively thin there are large optic ventricles which are not separated from the aqueduct. The infundibular region and the thalamus proper are small. The epi- thalamus includes a pair of habenular ganglia connected by a commissure as in all vertebrates. There are two outgrowths from the habenular region: a well developed epiphysis {pineal organ), anterior to which is a smaller parietal body. These two organs, arising from a common origin, were prob- ably originally paired, since the pineal body is in intimate relation with the right habenular ganglion, and the parietal body with the left. ^•Velum Interpositum of 4th Ventricle Velum Interpositu of 3rd Ventricle E2^S£££L. - Medulla Infundibulum Corpus Striatum-; Olfactory Lobe- ** Hypophysis Fig. 649. Sagittal section diagram of the brain of an amphibian. (After Edinger.) The presence in certain fossil fishes, for example Titanichthys, of a pair of foramina located side by side in the skull directly above this region in the brain, also seems to point to the originally paired relation of these organs. Apparently the tandem-like position of the pineal and parietal bodies in cyclostomes is the result of a secondary displacement of the former side-by- side arrangement. The histological structure of the epiphysis, or pineal body, as well as its access to light through a foramen in the dorsal region of the skull, seems to indicate that it is, in cyclostomes at least, a photoreceptive organ by means of which light and darkness are distinguished. Parietal Lobex -Cerebellum Paraphysis JH^^^^r=rM^M ^\. I ftfffcer-Vdum In Pallium *>~^^0^*~ ^3/// Velum Interpositum of-^^;-- Third Ventricle ^f=^r£-L _ ... ^£-3fe--i-r^hr--j555oBk ^ V _JJlllllfiy Medulla Corpus Striatum-£=-r-^-_-_r:r:r. Olfactory Lobe-ISH^'^ "^^^y^T^^^^^^^^r-lnf
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