. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. THE BRAIN 171 The olfactory lobes may be well marked or entirely invisible externally. In such forms as Anguis, Amphisbsena and Typhlops they are closely applied to the hemispheres, while in others {, Hatteria, Lacerta, Crocodilus) each consists of a well-marked olfac- tory tract, passing anteriorly into an olfactory bulb from which the nerves of smell arise. Olfactory ventricles are usually present. The thalamencephalon is always depressed, and is hardly, or not at all, visible from the dorsal side. A distinct hyp
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. THE BRAIN 171 The olfactory lobes may be well marked or entirely invisible externally. In such forms as Anguis, Amphisbsena and Typhlops they are closely applied to the hemispheres, while in others {, Hatteria, Lacerta, Crocodilus) each consists of a well-marked olfac- tory tract, passing anteriorly into an olfactory bulb from which the nerves of smell arise. Olfactory ventricles are usually present. The thalamencephalon is always depressed, and is hardly, or not at all, visible from the dorsal side. A distinct hypophysis and. Fig. 141.—Lonoitudisal Section through the Paeietal Eye and its C(J^- NECTiVE-TissuE Capsule OF Hatteria punctata. (After Baldwin Spencer.) cp, connective-tissue capsule ; r, "lens ;" cv, cavity of the eye, filled with fluid ; )'\ retinal portion of the vesicle ; va, blood-vessels ; c. n, cells in the nerve stalk (). infundibulum as well as an epiphysis are present, and in Lizards the parietal organ retains more or less distinctly, even in the adult, its primitive structure as a median eye. This jparietal eye (Fig. 141) is situated in the parietal foramen of the skull, and is in close connection with the epiphysis, though in the embryo the nerve which supplies it is seen to arise in- dependently from the brain, in front of the pineal outgrowth. The eye has the form of a vesicle, the dorsal wall of which may become thickened to form a transparent lens-like body, while the rest of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wiedersheim, Robert, 1848-1923; Parker, William Newton, 1857-1923. London, Macmillan
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