526 RESPIRATORY APPARATUS IN MAMMALIA. 



Communicating Orifice of the Sinuses with the Nasal Fossa. — All 

 the sinuses of one side communicate with the corresponding nasal fossa, by the 

 curved slit at the bottom of the middle meatus. This slit penetrates the superior 

 maxillary sinus, under the septum that separates it from the frontal sinus ; it 

 also entere the inferior maxillary sinus, which thus communicates solely with the 

 nasal cavity, while the other diverticuli open in common into this cavity, through 

 the medium of the superior maxillary sinus. 



Mucous Membrane of the Sinuses. — In entering the sinuses to cover 

 their walls, the pituitary membrane becomes extremely thin, and loses its great 

 vascularity ; it is applied immediately to the bones, and serves as a periosteum. 

 It has some nerves which terminate in small bell-shaped organs (Inzani). 



Development of the Sinuses. — -These cavities begin to be developed in 

 the foetus, and are gradually formed in the thickness of the bones they occupy. 

 They increase during the animal's lifetime, by the thinning of the bony plates 

 enclosing or partitioning them, and particularly by the growth of the superior 

 molar teeth, the roots of which project into them. The formation of the inferior 

 maxillary sinus is more tardy than the others ; though it is not so late as seven 

 or eight yeare, as the majority of Veterinary Anatomists have asserted. Goubaux 

 has proved that the sinus is already present in a six-months-old animal ; and in a 

 head which has been for several years in the museum of the Lyons School, and 

 which belonged to a foal of very small stature, about a year old, this sinus is 

 found, in its external part, to be already 1^ inches in depth, and -^ of an inch 

 in width. 



Functions of the Sinuses. — Have the sinuses or diverticuli of the nasal 

 cavities, the same uses as these cavities ? It is probable, although not absolutely 

 certain. There is nothing to prove that they have anything to do with respira- 

 tion or olfaction ; and it would seem that their exclusive function is to give 

 increased volume to the head without increasing its weight, and in this way to 

 furnish wide surfaces of attachment for the muscles belonging to this region — 

 these cavities being all the more ample as the muscles are large and numerous. 



Differential Characters in the Nasal Cavities of the other Animals. 



1. Nostrils. — la the Ox, the nostrils, placed on each side of the muflfle, are narrower and 

 less movable than in the Horse. (The superior extremity of the ala is not horizontal; the 

 inferior is divided into two br.mehes.) 



In the Pig, the end of the nose constitutes the snout (rostrum suis), the anterior surface of 

 which, plane and orbicular, shows tiie externul orifices of the nostrils. This snout— a veritable 

 tactile organ employed by the animal to dig up the ground — is covered by a dark-coloured 

 skin, kept damp by a humid secretion, like the muffle of the Ox. It hits for base the scooping- 

 fco?ie— a particular piece situated at the extremity of the nasal septum, and enveloped by a 

 layer of cartilage that extends around the nostrils. It is easy t) distinguish two symmetrical 

 halves in this bone, which evidently represent the two cartilages in the nose of Solipeds. 



In the Dog, the end of the nose forms a salient region, which is roughened, naked, usually 

 dark-coloured, damp, and sometimes divided by a medinn groove; in this region the nostrils 

 are fdaced, their form resembling two commas oppose i to each other by their convexities. 

 The cartilaginous framework sustaining these orifices is not composed of separate pieces, but 

 is oidy a dependency of the median septum and the appendages of the turbinated bones. 



The same considerations apply to the nostrils of the Cat, with the exception of tlie colour 

 of the integument, which is nearly always of a rosy hue, like the mucous surfaces. 



2. Nasal Cavities. — The nasal fosssB of the Ox, Sheep, and G-oat, are distinguished by 

 the presence of a third turbinated bone — the olfactory antrum, and by the communication 

 existing between tliem, posteriorly, above the inferior border of the vomer. We have already 

 seen that in these animals, as in those yet to be mentioned, the canal of Jacobson passes 

 completely through the palatine arch. 



