RESPIRATORY ORGANS. 243 
I]. RESPIRATORY ORGANS. APPARATUS RESPIRA- 
TORIUS. 
The organs of respiration consist of the nasal cavity, the 
nasopharynx, the pharynx (also a food-passage), the larynx 
(also the organ of the voice), the trachea, the bronchi, and the 
lungs. With them are usually described also the thyroid and 
thymus glands. 
1. The Nasal Cavity. Cavum nasi.—The osseous frame- 
work of the nasal cavity has already been described (page 59), 
and in connection with this description the boundaries of the 
cavity and its connections with other cavities have been given. 
It consists essentially of a large cavity bounded by the facial 
bones and divided by a longitudinal partition into two lateral 
halves. The two cavities thus formed are nearly filled by (1) 
the labyrinths of the ethmoid (ethmoturbinals), (2) the superior 
nasal conchz or nasoturbinals, projecting into the dorsal part 
from the ventral surface of the nasal bones, and (3) the inferior 
nasal conche, or maxilloturbinals, projecting into the ventral 
portion from the medial surfaces of the maxillaries. 
There remain to be considered, in addition to the bones, 
the cartilaginous framework of certain parts of the nose, and 
the mucous membrane. The lamina perpendicularis is con- 
tinued by cartilage, especially craniad, in such a way as to 
make a complete septum separating the two cavities. This 
septum extends from the septum of the external nose caudad 
to the lamina cribrosa, and from the internasal suture ventrad 
to the vomer and the suture of the premaxillaries. All parts 
of the nasal cavity are lined by mucous membrane. This is 
continuous at the nares with the integument, while at the 
choane it passes into the mucosa of the pharynx. It covers 
the conche nasales and the labyrinths of the ethmoid, passing 
into the cellules of the latter. Owing to the crowding together 
of the conche nasales and the labyrinths the nose is almost 
completely filled, only three narrow passageways being distin- 
guishable. The ventral one of these, known as the ventral or 
inferior meatus of the nose, lies ventrad of the inferior nasal 
concha, next to the nasal septum. It passes caudad beneath 
