32 MAMMALIA. 



a vestige of a third, and has its crystalline fixed by the ciliary processes 

 its sclerotic is simply cellular. 



The ear always contains a cavity called the tympanum, or drum, 

 which communicates with the mouth by the Euslachian tube; the 

 cavity itself is closed externally by a membrane called the membrana 

 tympani, and contains a chain of four little bones, named the incus or 

 anvil, malleus or hammer, the os orbiculare or circular bone, and the 

 stapes or stirrup ; a vestibule, on the entrance of which rests the 

 stapes, and which communicates with three semicircular canals ; and, 

 finally, a cochlea, which terminates by one canal in the vestibule, and 

 by the other in the tympanum. 



Their cranium is subdivided into three portions ; the anterior is 

 formed by the two frontal and ethmoidal bones, the middle by the two 

 ossa parietalia and the os ethmoides, and the posterior by the os occi- 

 pitis. Between the ossa parietalia, the sphenoidalis, and the os occipitis, 

 are interposed the two temporal bones, part of which belongs properly 

 to the face. 



In the foetus, the occipital bone is divided into four parts : the sphe- 

 noidal into two halves, which are again subdivided into three pair of 

 lateral wings ; the temporal into three, one of which serves to complete 

 the cranium, the second to close the labyrinth of the ear, the third to 

 form the parietes of the tympanum, &c. These bony portions, still 

 more numerous in the earliest period of the foetal existence, are united 

 more or less promptly, according to the species, and the bones them- 

 selves finally become consolidated in the adult. 



Their face consists of the two maxillary bones, between which pass 

 the nostrils ; the two intermaxillaries are situated before, and the two 

 ossa palati behind them ; between these descends the vomer, a bony 

 process of the os ethmoides; at the entrance of the nasal canal are 

 placed the ossa nasi ; to its external parietes adhere the inferior tur- 

 binated bones, the superior ones which occupy its upper and posterior 

 portion belonging to the os ethmoides. The jugal or cheek-bone unites 

 the maxillary to the temporal bone on each side, and frequently to the 

 os frontis ; finally, the os unguis and pars plana of the ethmoid bone 

 occupy the internal angle of the orbit, and sometimes a part of the 

 cheek. In the embryo state these bones also are much more subdivided. 



Their tongue is always fleshy, connected with a bone called the 

 os hyoides, which is composed of several pieces, and suspended from the 

 cranium by ligaments. 



Their lungs, two in number, divided into lobes, and composed of an 

 infinitude of cells, are always enclosed, without any adhesion, in a 



