THE LARYNX. 449 



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, that 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 

 thickness of the palatine arch. A wide orifice at the base of the maxillary turbinated 

 bone affords a communication between this sinus and the nasal fossa. 



In the Sheep and Goat, there exists a similar arrangement of 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 fla^ened 

 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, called 

 vibrissss. 



The cavities or nasal fossx offer nothing paiticular ; as in animals, they show a superior, 

 middle, and inferior rneatus. On their floor, 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 o;i its Schneideriau 

 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 spheuoidal sinus and the posterior ethmoidal cells, that open 

 beneath the roof of the nasal fossse; 2, The middle ethmoidal cells, opening into the 

 superior meatus; 3, The -anterior ethmoidal cells, and frontal and maxillary sinuses, 

 communicating with the middle ineatus. 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 bronchice terminating it. 



* . Larynx. (Figs. 227, 228, 229.) 



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

 general disposition of the larynx (Fig. 224 . 2. Isolate the cartilages, to examine 

 their external conformation. 3. Remove the muscles from a third larynx, to show the 

 mode of articulation of the various cartilages (Figs. 227, 228X 4. Prepare the muscles in 

 conformity with the indications furnished by a glance at figure 229. 5. Remove a larynx 

 as carefully as possible, so as not to injure the walls of the pharynx, in order to study 

 the interior of the organ, and especially its pharyngeal opening. 



Form Situation. The larynx forms a very short canal, which gives 

 passage to the air during respiration, and is at the same time the organ 

 of the voice. 



It is a cartilaginous box, depressed on each side, and open from one end to 

 the other : the anterior orifice being situated at the bottom of the pharyngeal 

 cavity, and the posterior continuous with the trachea. 



This apparatus, situated in the intermaxillary space, is suspended 

 between the two cornua of the os hyoides, and fixed to the extremities of 

 these appendages by one of its constituent pieces. It serves to support the 



