Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/914/
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 alæ 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 interiorly, so as to form a roof over 
the optic nerves. 
The tethmoid, Owen (anterior sphenoid, Cuv. : 
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 oethmoid 
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 oethmoid itself. In the Mammalia, 
owing to the prodigious developement of the 
olfactory apparatus, the athmoid 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 oethmoid, 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 ; (athmoid, 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 oethmoid 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 1 
consequence of the construction of their nose 1 
quite wanting in Fishes, must not be omitted I 
in enumerating the elements composing the 1 
skull in higher animals. In the humbler Rep- 1 
tiles, indeed, no traces of it are distinguishable ; 1 
but when the olfactory apparatus becomes fully 1 
developed, as in the Mammalia, they form an I 
important part of the nasal character, and are ;| 
found of large size, connected inseparably with j 
the bones that surround the nose. 
The bones of the face have been already J 
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 1 
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, j 
which in them are principally implanted upon 
the intermaxillary (17) that form the greater 
portion of the upper jaw. The maxillary 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 j 
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 this 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 Chondropterygii, 
nevertheless, they are mere rudiments imbedded 
in the substance of the upper lip. They are j 
persistent throughout all orders of Reptiles, I 
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
        

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