. The Journal of comparative neurology and psychology. Figs. 25, 28, 29, 30 show this in sections and models. By the time the optic ridge is formed the floor of the forebrainvesicle has become depressed to form broad primitive inferior lobesand in the caudal wall of this a mammillary recess marks the begin-ning of the mammillary bodies (Figs. 26 and 27). This is bounded Johnston, Forebrain Vesicle in Vertebrates. 495 caudally by the tuberculum posterius. Later, when the hypophysisHas reached its definitive position a saccus outgrowth from theinferior lobes appears and the region at which it is
. The Journal of comparative neurology and psychology. Figs. 25, 28, 29, 30 show this in sections and models. By the time the optic ridge is formed the floor of the forebrainvesicle has become depressed to form broad primitive inferior lobesand in the caudal wall of this a mammillary recess marks the begin-ning of the mammillary bodies (Figs. 26 and 27). This is bounded Johnston, Forebrain Vesicle in Vertebrates. 495 caudally by the tuberculum posterius. Later, when the hypophysisHas reached its definitive position a saccus outgrowth from theinferior lobes appears and the region at which it is connected withthe brain may be called the infundibulum. There are therefore inthe floor of the forebrain vesicle four recesses formed as in selachians:terminal pit or preoptic recess, primitive optic groove or postoptierecess, infundibulum and mammillary recess. The fonnation of the velum transversum, epiphysis and para-physis need not be described as they are already known (Minot andothers). These structures are represented in Figs. 30, 31, 32, Fig. 33. Amblystoma p., all the chief features of the forebraiu sagital section, x 40. 5. Beptiles and have to say here only that the study of whole mounts of chickembryos between 20 and 40 hours of incubation shows that the samerelations exist in the region of the optic chiasma as in Squalus andAmblystoma. In early embryos the optic vesicles are connectedby a primitive optic groove behind the terminal ridge. Later, theoptic ridge is formed, the terminal pit becomes connected with thecavities of the optic stalks, and the optic chiasma occupies theterminal ridge. 6. chief peculiarity of the mammalian brain is the great size ofthe cerebral hemispheres. In the adult, as is well known, there is 496 Journal of Comparative Neurology and Psychology. SL membraneous tela over the median ventricle and this is continuedas the roof of the interventricular foramen into the wall of eachhemisphere. In front o
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