234 NERVOUS SYSTEM. 



tious without, and presents internally radiating fasciculi of 

 white nervous fibres extending peripherad from its base. 

 The great transverse commissure of the cerebellum, or the 

 pons Varolii is still wanting, like the cerebellic hemispheres. 

 The optic lobes (97- C. d, e,) reduced in their proportions, 

 and provided with internal ventricles (e,) are partially encom- 

 passed on their fore part by the large tapering hemispheres. 

 The cerebral hemispheres (97- D. d,) destitute of convolu- 

 tions, smooth and cineritious externally, hollow within, (97. 

 C. g,) present internally the thalami optici and corpora 

 striata (^,) and a distinct choroid plexus, (9J. C. h,) towards 

 the median side of their contained ventricles. These hemi- 

 spheres are broad and short in the crocodilian reptiles, and 

 more lengthened, narrow, and tapering forwards in the in- 

 ferior tribes, especially in the chelonia. Rudiments of cere- 

 bellic hemispheres are also seen in the crocodiles. The ol- 

 factory tubercles (97- D. g,) are much smaller than in fishes, 

 cineritious externally, and placed in contact with the cerebral 

 hemispheres. On the inferior surface of the brain in the 

 chelonia (97- D,) we observe an intimate union and decussa- 

 tion of the optic nerves (97. D./,) and behind these a long 

 tubular hypophysis (97. D. e,) or continuation of the third 

 ventricle into the infundibullum and petuitary gland. The 

 pineal gland (97- C./,) is still exposed on the upper part of 

 the brain between the optic lobes and the cerebral hemi- 

 spheres. All the parts of the brain are more compacted to- 

 gether in reptiles than in lower vertebrata ; the ganglia of the 

 posterior or sensitive roots of the spinal nerves are now more 

 conspicuous, like the lateral and splanchnic ganglia of the 

 sympathetics ; and the spinal nerves come off more nearly 

 opposite to the places of their respective destinations than in 

 the lower classes. 



The nervous system of birds presents only a more elevated 

 condition of the same plan of structure already developed in 

 the crocodiles and inferior reptiles. The great centres of the 

 nervous system in the vertebrated animals like those of the 

 vascular, are at first developed in a lineal direction and ex- 

 tended longitudinally, as we see in the fishes, but at 

 length acquiring encreased lateral development, these parts, 

 in both systems become compacted together and accumulate 

 upon each other to form a more, short, circumscribed and 



