448 TEE RESPIRATORY APPARATUS IN MAMMALIA. 



the foetus, and are gradually hollowed in the thickness of the bones which 

 concur to form them. They increase during the animal's lifetime, by the 

 thinning of the bony plates inclosing or partitioning them, and particularly 

 by the growth of the superior molar teeth, whose roots project into these 

 cavities. The formation of the. inferior maxillary sinus is more tardy than 

 the others ; though it is not so late as seven or eight years, as the majority of 

 Veterinary Anatomists have asserted. M. Goubaux has proved that the sinus is 

 already present at six months old ; 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 seen, in its external part, 

 to be already 1J> inches in depth, and 8-10ths 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 rlo 

 with respiration 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 insertion for the muscles attached 

 to this bony region these cavities being all the more ample as the muscles 

 are large and numerous. 



DIFFERENTIAL CHARACTERS OF THE NASAL CAVITIES IN OTHER THAN SOLIPED ANIMALS. 



1. Nostrils In the Ox, the nostrils, placed on each side of the muffle, are narrowef 

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

 the inferior is divided into two branches.) 



In the Pig, the end of the nose constitutes the snout (rostrum suis\ whose anterior 

 surface, plane and orbicular, shows the external 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 has 

 for a base the scooping-bone, a particular piece situated at the extremity of the nasal 

 septum, and enveloped by a layer of cartilage which extends around the nostrils. It is 

 easy to distinguish two symmetrical halves in this bone, which evidently represent the 

 two cartilaginous pieces 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 median groove ; in this region 

 the nostrils are pierced, their form resembling two commas opposed to each other by their 

 convexities. The cartilaginous framework sustaining these orifices is not composed of 

 separate pieces, but is only a dependance 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 the 

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



2. Nasal Cavities. The nasal fossae of the Ox, Sheep, and Goat are distinguished by 

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

 existing between them, 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 

 completely traverses the palatine arch. 



In the Pig, the nasal fossse 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 Ibssre, without 

 concurring in the formation of the sinuses. 



3. Sinuses. In the Ox, the frontal sinuses are prolonged into the bony cores which 

 support the horns, and into the parietal and occipital bones ; they therefore envelop, in 

 a most complete manner, the anterior and superior part of the cranium, and form a 

 double wall to this bony receptacle. They are extremely diverticulated, and do not 

 communicate with those of the great maxillary bones. They usually open, on each side, 

 into the nasal cavities by four apertures pierced 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 

 the frontal sinuses are designated the orbital sinuses. 



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

 email, and are in communication with the preceding. 



