BIKDS. 365 



cavities are spacious and open behind by a fissure in the palate. 

 Frontal sinuses are not present in birds. Within the nasal cavity 

 on each side are found three laminae, usually cartilaginous, some- 

 times bony; of these the middle one has more or fewer spiral 

 convolutions, the lowest is always very small. These laminae 

 correspond to the conchce or spongy bones (ossa turbinata) of mam- 

 mals; they are covered by a velvetty mucous membrane. The 

 olfactory nerves penetrate the nasal cavities undivided, without 

 first passing through a cribriform plate (peculiar to mammals). 

 They divide in the cavity into many fine branches, which spread 

 themselves over the septum and upon the upper conch, which 

 especially is the seat of the sense of smell, and of which the size 

 appears to increase with the fineness of this. The inferior conch 

 receives its nerves from the first branch of the fifth pair alone. 

 According to the anatomical investigations and experiments of 

 SCARPA on birds, the waders would seem to have the finest smell, 

 and then the water-birds, the birds of prey, and the climbers, 

 whilst this sense is dullest in the singing and the gallinaceous 

 birds. Also, according to this great anatomist, the males are some- 

 what more acute in smelling than the females. To the olfactory 

 organ a pair of glands also belongs, which JACOBSOX and NITZSCH 

 have brought into fuller notice. Not in water-birds only, but nearly 

 in all birds there is found on the frontal bone, or above the margin 

 of the orbit, or within it, a gland on each side, of which the ex- 

 cretory duct runs to the cavity of the nose. The fluid which it 

 secretes is watery, and seems to resemble that of the tears \ 



The organ of sight is highly developed. In this class no ex- 

 amples are met with of species which have eyes either small or 

 covered by the skin, and thus unfit for seeing, as is the case in 

 certain species of the other classes of vertebrate animals. On the 

 contrary, the eyes in birds are large, especially in the birds of prey. 

 With the exception of the nocturnal birds of prey, where they are 

 directed forward, they are placed laterally, above the angle of the 

 bill, or more towards the back part of the head on each side, as in 

 the snipes. The eye-ball before and behind is circumscribed by a 

 spherical segment, but the anterior segment belongs to a smaller 



1 JACOBSOX Bulletin de la Soc. philomatique, Avril, 1813; C. L. NITZSCH in 

 MECKEL'S Archivfiir die Physiol. vi. 1820, s. 234 269. 



