. An elementary course of practical zoology. Zoology. 144 THE DOGFISH marked difference between the brain of the dogfish and that of the frog is seen in its anterior portion. In the frog, the diencephalon is con- tinuous anteriorly with the paired cere- bral hemispheres (159, Fig. 49): in the dogfish there is in this region a relatively smaller, unpaired por- tion of the brain, marked in front by a slight groove, and known as the prosen- cephalon ( FiY), which represents the cere- bral hemispheres of the higher Verte- brates but which does not become subdi- vided externally into paired lobes.
. An elementary course of practical zoology. Zoology. 144 THE DOGFISH marked difference between the brain of the dogfish and that of the frog is seen in its anterior portion. In the frog, the diencephalon is con- tinuous anteriorly with the paired cere- bral hemispheres (159, Fig. 49): in the dogfish there is in this region a relatively smaller, unpaired por- tion of the brain, marked in front by a slight groove, and known as the prosen- cephalon ( FiY), which represents the cere- bral hemispheres of the higher Verte- brates but which does not become subdi- vided externally into paired lobes. Ante- riorly it gives off, right and left, a large, oval olfactory lobe (Z. ol) each connected with the prosen- cephalon by a short, stout stalk {Tro) and applied distally to the corresponding ol- factory capsule. The prosencephalon contains paired lateral ventricles, which. mi Fig. 115.—Dorsal view of the brain of Scylliuvi caniculd. The posterior division of the brain is the medulla oblongata (JV/f), enclosing the fourth ventricle i^). The large cerebellum {HH') nearly covers the optic lobes (^MH ) The diencephalon (JZH') shows in the middle the third ventricle, and the place of attachment of the pineal stalk (G/>). The prosencephalon {VH') gives off the olfactory lobes (JFro. ). The origins of the following nerves are shown:—optic (//), trochlear (/K), trigeminal (F), facial (F//), auditory (^///), glossopharyngeal {IX), and vagus Cx). (From Wiedersheim's Anatomy.). 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Parker, William Newton, joint author. London, Macmillan and Co. , Limited; New York, The Macmillan Company
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