NERVOUS SYSTEM. 239 



of the superficial parts of the face, and the magnitude of the 

 acoustic nerve, with the great development of their internal 

 ear and their acute hearing, especially in nocturnal birds. The 

 glosso-pharyngeal passes as usual to the tongue and pharynx, 

 the hypo-glossal chiefly to the root of the tongue and upper 

 larynx, and the pneumo-gastric, communicating at the base of 

 the cranium with the accessory, descends with the jugular 

 vein along the neck to be distributed on the lungs, the in- 

 ferior larynx, the oesophagus and stomach, especially the 

 ventriculus succenturiatus. The spinal nerves are chiefly 

 cervical and sacral, from the number of vertebrae composing 

 these parts of the column, and the brachial and lumbar 

 plexuses are formed and distributed on the arms and legs, 

 nearly as in quadrupeds. The sympathetic, greatly encreased 

 in its development, presents distinct lateral ganglia from the 

 base of the skull to the end of the coccyx, it unites anteriorly 

 with the pneumo-gastric, the facial and the trigeminal nerves, 

 and at its posterior end the lateral ganglia become approxi- 

 mated and united on the median plain under the coccygeal 

 vertebra. It forms distinct ganglia and plexuses around the 

 great arteries, for the viscera of the trunk ; its cervical por- 

 tion is protected, along with the vertebral arteries, in the 

 foramina of the transverse processes ; and it is every where 

 connected by anastomosing filaments with the spinal nerves 

 along the sides of the vertebral column, as in other classes. 



In the mammiferous animals a higher grade of the develop- 

 ment of this system is perceptible in the magnitude and ex- 

 tension of the spinal chord, and of the cerebral and cere- 

 bellic hemispheres, in the encreased number of internal 

 cineritious deposits in all parts of the white fibrous spino- 

 cerebral axis, in the more complete union of all the lateral 

 parts of this axis by means of decussating fasciculi and 

 various commissures of converging fibres, in the encreased 

 size and approximation of the ganglia on all the symmetrical 

 sensitive nerves, and in the more methodical and extensive 

 distribution of the great sympathetic, and its appropriation to 

 individual organs. The spinal chord, though encreased in its 

 proportion to the bulk of the body, is now less in proportion 

 to the cerebral mass than in the inferior classes ; its internal 

 longitudinal canal has almost become obliterated ; its lateral 

 halves are more intimately united together, and the crescentic 



