NERVOUS SYSTEM. 89 



supply the eyelids and lacrymal gland. The course of the inferior 

 maxillary or third branch of the fifth is very simple, entering the 

 canal of the lower jaw, and ramifying, as may be most distinctly 

 seen in the Duck, beneath the horny texture of the mandible ; it 

 gives off no gustatory branch to the tongue. The small root of the 

 trigeininal nerve passes over the ganglion, and distributes twigs, as 

 in the Mammalia, to the manducatory and hyoid muscles. The 

 third, fourth, and sixtn nerves correspond with those of the Mam- 

 malia, and supply the muscles of the eye ; their mode of origin 

 from the brain is the same as in Man, and their cerebral roots ad- 

 mit of being easily traced. The large muscles of the nictitating 

 membrane are supplied in birds by nerves from the sixth pair, or 

 abducens. The seventh pair, or portio dura, is, as might be pre- 

 mised from the absence of facial muscles, only feebly developed, and 

 as usual united with the portio mollis or auditory nerve. The 

 eighth, or glosso-pharyngeal, is more remarkable, and differs in 

 several important relations from the same nerve in Man and the 

 Mammalia. It is more intimately united than in them both in its 

 origin and course with the nervus vagus, and gives off, in common 

 with the latter, several branches to the pharynx and upper part of 

 the larynx, parts which in the Mammalia are supplied from the ner- 

 vus vagus only. The most important branch however of the 

 eighth is the largest, which is distributed to the tongue, and may be 

 traced in birds of a delicate sense of taste into the papillae of that 

 organ, serving unquestionably in such cases to the exercise of the 

 gustatory function. At all events, this nerve, as well as the vagus, 

 is of a mixed character, being both motor and sensitive. The va- 

 gus gives branches to the muscles of the tongue, descends the neck 

 by the side of the jugular vein, and forms plexuses, from which 

 branches proceed to the pharynx, lungs, stomach, and proventriculus, 

 while recurrent branches are distributed to the muscles of the inferior 

 larnyx. The nervus accessorius soon unites within the cranium with 

 the vagus. The hypoglossal nerve, or ninth pair, arises by two roots, 

 and gives branches to the muscles of the tongue, which are particu- 

 larly developed in the Woodpeckers, and others of large size, to the 

 sterno-tracheal muscles. 



The brachial plexus is formed in birds by the two last cervical and 

 two first dorsal nerves. The nerves of the lower extremity proceed 

 from an anterior and posterior plexus, that of the lumbo-sacral nerves 

 forming the ischiatic nerve. The number of spinal nerves generally 

 corresponds with that of the vertebrae. 



