OSSEOUS SYSTEM OF MAMMALIA. 37 



in its dimensions, occupies the centre, and the zygomatic process of the 

 temporal bone forms the posterior part of the arch. The arch, in these 

 animals, varies greatly in strength and form. In the spotted Cavy it is 

 expanded to an extraordinary degree, but it is thin, and internally concave. 

 In the Capybara, Coipus, and Beaver, it is very strong and extensive ; as 

 might be expected in animals capable of using their teeth so effectually. 

 In the Squirrel it is of moderate strength ; in the Rat it is slender ; in the 

 Hare it is strong, from its breadth, but is compressed, and forms the lower 

 margin of the s enormous orbit. Turning from these animals to the Car- 

 nivora, we find the zygomatic arch of great extent and stoutness, and 

 consisting of a long process of the malar bone, overlaid by the usual 

 process of the temporal bone, which is bold and strong : the zygoma, 

 moreover, does not only take a simple arched sweep backward, but 

 is arched upward also, by the bending down of each extremity, the 

 line of anterior declination falling precisely on the centre of the lani- 

 ary molar (carnassiere), the point in which the force of the jaws is con- 

 centrated. It will be evident that the muscular fibres arising from the 

 lower edge of this arch are straining, when in action, against that modi- 

 fication of form which enables inert bodies to bear the greatest weight, 

 or application of power. In these animals, the ball of the eye, seated 

 in an orbit exposed and open, is protected by ligamentous expansions, 

 which, in a certain sense, isolate it, and its own muscular apparatus. It 

 is, however, more immediately affected by the violent contraction of the 

 temporal muscle, in ferocious, than in graminivorous Mammalia; and 

 starts forward, whilst they rend the flesh of their victims, so as to pro- 

 duce an expression of the most implacable fury. 



Proceeding from the orbits, or recesses, of the organs of vision, to the 

 nasal cavity, it may be stated, that this cavity occupies the space partly be- 

 tween, and partly below, or before, the orbits. It is covered, externally, by 

 the two nasal bones (consolidated, in the Monkeys, into one), and is divided, 

 internally, by a longitudinal septum, or partition, formed by a vertical 

 plate of the ethmoid bone and the vomer : the floor of this divided cavity 

 consists of the palatal plates of the superior maxillary bones, and be- 

 hind those, of the true palate bones ; which, together, constitute the roof 

 of the mouth. The nasal cavities open, anteriorly, by the two nostrils, 

 a cartilaginous septum being continued from the osseous division within. 

 Posteriorly, they open into the fauces, or throat, by two canals, termed 

 posterior nares. A duct, also, from the inner angle of each orbit, leads 

 into each nasal cavity, for the purpose of conveying the tears, or fluid, 

 secreted to wash the eye : hence it is termed the ductus lachrymalis. 

 The interior of the nasal cavities is filled with the turbinated processes 

 of the ethmoid bone, and also with the two inferior spongy or turbinated 

 bones, of which the shape can scarcely be described, otherwise than by 



