SEC. IV ANATOMY OF BIRDS 263 



one or two usually counted as dorsal, which combine to form a 

 single cord, whence the nerves of the wing are derived. Similar 

 network of three to five true sacral nerves furnishes the nerves of 

 the leg. 



The Sympathetic System consists of a pair of nervous cords 

 running lengthwise below the bodies of the vertebrae, one on each 

 side in the trunk, and in corresponding relations with cranial bones. 

 An extensive and intricate series of communications is effected with 

 the nerves of the cerebrospinal system, excepting the special-sense 

 nerves of smell, sight, and hearing. The points of communication 

 form a chain of sympathetic ganglia ; from these knots' the most 

 conspicuous features of the system, nervous cords pass to their dis- 

 tribution in the motory mechanism of the heart and blood-vessels 

 and other viscera. The anterior sympathetic nerves are the iridian; 

 the anterior ganglia are the sphenopalatine or Meckelian, intimately 

 connected with cranial nerves. The system ends behind in the 

 caudal region of the spine by a ganglion impar. 



Sense of Smell : Olfaction. — The sense of smell is effected by 

 terminal branches of the olfactory (1st cranial) nerve, ramifying in 

 the mucous (pituitary or Schneiderian) membrane of the nasal 

 cavities. Owing to the comparatively small size and little com- 

 plexity of the foldings and pleatings of bone or cartilage in the 

 nasal chambers, the sensory surface being correspondingly limited, 

 it is not probable that birds possess this sense in a high degree. 

 Besides the cartilaginous or osseous septum, generally more or less 

 complete in birds, there are lateral scrolls and whorls of bone in 

 endless diversity in most birds, which may be ossified, or remain 

 gristly. The general cavity is mostly bounded and enclosed by the 

 bony beak ; floored by the anterior part of the hard palate ; 

 defended on each side by the descending prong of the nasal bone ; 

 in the dry skull, it either seems continuous with the great orbital 

 cavity on each side behind, or is separated therefrom by lateral eth- 

 moid (prefrontal) or lacrymal ossifications, or both. Outwardly the 

 nasal chambers open upon the beak by the external nostrils. These 

 openings are minute or quite obliterated in some Steganopodes, as 

 pelicans and cormorants. The nasal cavities always communicate 

 with the back part of the mouth by the posterior naves (Lat. naris, a 

 nostril) ; they are generally paired, that is, with a partition between 

 them, sometimes united in one median aperture. The olfactory 

 nerve, which is rather a prolongation of the rhinencephalon itself 

 than an ordinary nerve, escaping from the brain-box by a special 

 foramen, traversing the upper part of the interorbital septum in a 

 groove or canal, enters the nasal cavity by a single orifice (excepting 

 Apteryx and Dinornis), instead of the numerous apertures in a cribri- 

 form plate by which its filaments reach their destination in mam- 



