830 



OSSEOUS SYSTEM. (CoMP. ANAT.) 



in reality they are distinct elements of the 

 skull. In the higher Vertebrata they are con- 

 solidated with the sphenoid, and have received 

 the names of alee minores or apophyses ingrassii. 

 Above these pass out the olfactory and beneath 

 them the optic nerves, a circumstance which 

 in itself sufficiently indicates their real nature. 

 Sometimes, as in the Carp, they are united 

 together inferiorly, so as to form a roof over 

 the optic nerves. 



The eethmoidjOwen (anterior sphenoid, Cu v. : 

 15,) so highly developed in the carnivorous 

 Mammalia, is in the lower Vertebrata reduced 

 to an extremely simple condition. In Fishes 

 (fig. 437) it is generally distinct enough, form- 

 ing the posterior boundary of the interorbital 

 septum, but sometimes it is quite wanting or 

 represented by membrane. When present, it is 

 generally placed upon the sphenoid, sending 

 off processes to join sometimes the ingrassial 

 bones, sometimes the alar bones, or occasionally 

 to remain suspended in the interorbital mem- 

 brane that unites all these parts. The cethmoid 

 appears to be deficient throughout all tribes of 

 Reptiles. In Birds it is recognizable as a bone 

 of considerable size, separating the posterior 

 parts of the orbits, which it assists in forming 

 the two lateral facets that enter into the com- 

 position of those cavities corresponding with 

 the ossa plana, as they are called, of the human 

 subject; but these are obviously only portions 

 of the cethmoid itself. In the Mammalia, 

 owing to the prodigious developement of the 

 olfactory apparatus, the tzthmoid becomes ex- 

 tremely increased in size and importance, 

 closing the anterior extremity of the cranial box, 

 where it is perforated so as to present a central 

 crest and cribriform plate, while inferiorly it 

 has superadded to its body the superior tur- 

 binated osseous lamella that enter so largely into 

 the construction of the olfactory organ. 



The vomer (16) is in Fishes a large and im- 

 portant bone, joined posteriorly to the sphenoid 

 and above to the cethmoid, forming a vertical 

 portion, on each side of which are situated the 

 organs of smell. Inferiorly it forms part of the 

 roof of the mouth, and is often armed with teeth. 

 Throughout all the Vertebrata this portion of the 

 skeleton holds an analogous position and is re- 

 cognized with facility. In Frogs and Lizards the 

 bone is double, but in Tortoises and the higher 

 animals generally there is but a single vomer, 

 which enters more or less into the composition 

 of the nasal septum. 



The nasal bones, Owen; (cethmoid, Cuv. : 

 3) in Fishes are represented by a single bone 

 impacted between the mid-frontals and the pre- 

 frontals, and inferiorly joined to the vomer, 

 forming a kind of septum between the nasal 

 organs, and thus in position resemble some- 

 what the vertical lamella of the (Ethmoid 1 of 

 Mammalia. Sometimes, as in the Eel and the 

 Conger, the bones in question are inseparably 

 united into one piece. In the higher animals 

 the nasal bones are two in number, covering 

 the nasal cavity like an arch. They are present 

 in all Reptiles except the Chelonians, and in 

 Birds and Mammals are easily recognizable 

 from their position. 



The inferior turbinated bones, although in 

 consequence of the construction of their nose 

 quite wanting in Fishes, must not be omitted 

 in enumerating the elements composing the 

 skull in higher animals. In the humbler Rep- 

 tiles, indeed, no traces of it are distinguishable ; 

 but when the olfactory apparatus becomes fully 

 developed, as in the Mammalia, they form an 

 important part of the nasal character, and are 

 found of large size, connected inseparably with 

 the bones that surround the nose. 



The bones of the face have been already 

 considered as constituting a very complex 

 framework, destined to lodge the organs of the 

 principal senses or to constitute the instruments 

 appropriated for the prehension or mastication 

 of food. Seeing, however, that the same bone 

 not unfrequently enters into the composition of 

 several distinct cavities, we are unable to classify 

 them further, and must therefore content our- 

 selves with enumerating them seriatim as they 

 occur to our notice. 



The maxillary (18) perform only a secondary 

 office in forming the upper jaw of a Fish, being 

 in the finny tribes generally destitute of teeth, 

 which in them are principally implanted upon 

 the intermaxillary (17) that form the greater 

 portion of the upper jaw. The nuixillan/ in 

 Fishes is moveably articulated with the inter- 

 maxillary, the vomer (16), and the palatine (22). 

 Sometimes, as in the Herring and Lepisosteus, 

 this bone is divided into several pieces. In 

 Skates and Rays the whole upper jaw is made 

 up of a single ossified mass, which bears the 

 numerous rows of teeth attached to its under 

 surface. 



But in all Reptiles, in Birds, and in Mam- 

 malia the maxillary bones form the principal 

 portion of the upper jaw, more particularly in 

 the Mammalia, where the intermaxillary bones 

 are comparatively of small size. In this portion 

 of the upper jaw are fixed the grinding teeth, 

 where such are present, a circumstance which 

 in itself demands great strength in this part of 

 the face; and, consequently, wherever power 

 of jaw is required to be conferred, it is prin- 

 cipally obtained by the increased developement 

 of tins element of the skeleton, which thus be- 

 comes the largest and, as it were, the central 

 bone of the whole fabric. 



The intermaxillary bones (17) form the prin- 

 cipal part of the upper jaw in Fishes, and upon 

 their shape depends that of the snout. Some- 

 times these bones are flattened horizontally, or 

 compressed laterally, or prolonged into a beak, 

 their form being modified by circumstances 

 in almost every genus. In the Chondroptery;j,ii, 

 nevertheless, they are mere rudiments imbedded 

 in the substance of the upper lip. They are 

 persistent throughout all orders of Reptiles, 

 Birds, and Mammals, until we arrive at the 

 Quadrumana, where they become anchylosed 

 with the maxillary, and in Man they are quite 

 obliterated at an early period. 



The bones of the face in osseous Fishes are 

 exceedingly numerous and irregular, neither is 

 it easy to identify many of them as being at all 

 analogous to those which normally make up 

 the face, even of those Reptiles which present 



