THE LARYNX. 527 



In the Pig, the nasal fossae are long and narrow. They are, on the contrary, very short 

 in the Dog aud Cat, and the internal cells of the turbinated l)oue8, reniarkiible for their 

 numl)er and complexity, all communicate witii the proper nasal fossae, without concurring in 

 the formation of the einusea. Tlic latter are divided by the vomer into two superposed com- 

 partments, very distinct fmm each other in tlieir posterior half; the superior is olfactory, the 

 inferior is respiratory. 



3 Sinuses. — In the Ox, the /ro«<aZ sinuses are prolonged into the bony cores which support 

 the horns, and into the parietal and occipital bones ; they therefore envelop, in a most com- 

 plete manner, the anterior and superior part of the cranium, ami form a double wall to this 

 bony cavity They are extremely livertieulated, and do not communicate witli those of the 

 snpermaxillary bones. They usually open, on each side, into tiie nasal cavities, by four 

 apertures at the biuse of the great ethmoidal cell. According to Girard, three of tluse orifices 

 lead to spicial oompartmenta, isolated from one another, and grouped around the orbit, in 

 consequence of which these diverticuli of tne frontal sinuses are designated the orbital sinuses. 



This author inis denied the presence of sphenoidal sinuses; but they exist, altliough small, 

 and are in communic.ition with the preceding. 



The sinus of the gifut ethmoidal cell comports itself as in the Horse. 



There is only one pair of maxillary sinuses, which are very large, and partitioned into two 

 compartments by a plate of bone ; this bears at ite superior border the supermaxillo-dental 

 canal, like the superior maxillary sinus of Solipeds. The external or maxillary compartment, 

 is prolonged into the lachrymal protuberance; the internal occupies tiie substance of the 

 palatine arch. A wide orifice at the base of the maxillary turbinated bone atibrds communica- 

 tion between this sinu.-s and the nasal fossa. 



In the Sheep and Goat, there exists a similar arrangemeut in the sinuses of the head; 

 but tliese cavities are mucli less spacious than in the Ox; the frontal sinus, in particular, does 

 not extend beyond the superior border of the frontal bone. 



In the Pig, these latter sinuses are prolonged into the parietal bones; though they are far 

 from oflferiug the same extent as in the smaller Rundnants. It is the same with the others; 

 they present an anangement analogous to those of the Sheep and Goat. 



In the Dog and Cat, there are only, on each side, a maxillary and a frontal sinus. The 

 first scarcely merits notice • aud the second, a little more developed, opens into the nasal 

 cavity by means of a small aperture situated near the middle septum of the two frontal sinuses. 



(l.eyh states that the Carnivora have no maxillary sinus; consequently, the sphenoidal 

 einus communicates below with the nasal fossae.) 



COMPAKISON OF THE NaSAL CaVITIES IN MaN WITH THOSE OF AnIMALS. 



The external orifices of the nasal cavities of Man are called nostrils; these are flattened 

 transversely, and prolonged in front of the lobule of the nose; their external face, or ala, 

 id concave and movable. They are lined internally by a membrane that holds a middle 

 place between the skin aud mucous membranes; it has a number of little hairs, called 

 vihrissx. 



The cavities or nasal fossx oft'er nothing [larticular; as in animals, they show a superior, 

 middle, aud inferior meatus. Ou their tio<ir. in front, is seen the superior orifice of the 

 incisive foramen, which corresponds to the commencement of Jacobson's canal. The pituitary 

 membrane has a squamous epithelium in its olfactory, as on its Sclineiderian portion. At the 

 bottom of the nasal cavities and the upper part of the pharynx, is a kind of diverticulum 

 named the posterior nares ; it has been already alluded to when speaking of the pharynx. 



The sinuses are: 1. Tlie sphenoidal sinus and the posterior ethmoidal cells, that open 

 beneath the roof of the nasal fossae. 2. The middle ethmoidal cells, opening into the superior 

 meatus. 3. The anterior ethmoidal cells, and frontal and maxillary sinuses, communicating 

 with the middle meatus. All these sinuses have a proper communicating orifice with the nasal 

 cavities. 



The Air- tube succeeding the Nasal Cavities. 



This single tube comprises : the larynx, which commences the trachea ; the 

 latter forms the body or middle poi-tioii, the bronchi terminating it. 



1. Larynx (Figs. 308, 311, 312, 313, 314). 



Preparation.— \. Make a longitudinal section f)f the head, in order to study the general 

 arrangement of the larynx (Fig. 308). 2. Isolate tiie cartilnges, to examine their external 

 conformation. 3. Remove the muscles from a third larynx, to show the mode of articulation 



