THE LARYNX. 527 



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

 in the Dog and Cat, and the internal cells of the turbinated bones, remarkable for their 

 number and complexity, all communicate with the proper nasal fossae, without concurring iu 

 the formation of the sinuses- The latter are divided by the vomer into two superposed com- 

 partments, very distinct from each other iu their posterior half; the superior is olfactory, the 

 inferior is respiratory. 



3. Sinuses.— In the Ox, the frontal amuses 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, and form a double wall to this 

 bony cavity. They are extremely iiverticulated, and do not communicate with those of the 

 supermaxillary bones. They usually open, on each side, into the nasal cavities, by four 

 apertures at the base of the great ethmoidal cell. According to Girard, three of these orifices 

 lead to special compartments, isolated from one another, and grouped around the orbit, in 

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



This author lias denied the presence of sphenoidal sinuses; but they exist, although small, 

 and are in communication with the preceding. 



The sinus of the great 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 its 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 the substance of the 

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

 tion between this sinus and the nasal fossa. 



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

 but these cavities are much 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 offering the same extent as in the smaller Ruminants. It is the same with the others; 

 they present an arrangement 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* and 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. 



(Leyh states that the Carnivora have no maxillary sinus; consequently, the sphenoidal 

 sinus communicates below with the nasal fossae.) 



Comparison 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, 

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

 place between the skin and mucous membranes; it has a number of little hairs, eaUed 

 vibrissas. 



The cavities or nasal fossas offer nothing particular ; as in animals, they show a superior, 

 middle, and inferior meatus. On their floor, in front, is seen the superior oriflce 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 Schneiderian 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. The 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 portion, the bronchi terminating it. 



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

 Preparation.— 1. Make a longitudinal section of the head, in order to study the general 

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

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



