SKELETON'. 



SKELETON. 



Olivary Proem*, and in front a pointed one, the Ethmoid Spine (6, 8) 

 which fits into the Ethmoid Bone. The sides of the body dope 

 obliquely downward* toward* the great alto, and the carernou* sinu* 

 and internal carotid artery of each aide reit against them. The poste- 

 rior surface (6, 7) of the body U rough, and unite* with the end of the 

 baailar process of the occipital. The anterior present* the opening* 

 of large cell* which occupy the whole interior. Thtae are divided by 

 a middle aeptum (a, 5), and are partly closed in by two small portion* 

 of bone called Sphenoids! Cornua ; where not thus closed, they open 

 into the posterior ethmoidal cells. The under surface of the body U 

 chiefly flat, but has a ridge called the azygous process along the middle 

 line, which fit* to the Vomer. 



The Greater Aim (2) are affixed by the sides of the body, and project 

 from it outwards, upwards, and forwards. On each there are three 

 principal surfaces, turned towards the brain, the temple, and the 

 orbit, repectively. The inner or cerebral (6, 8) U concave, support* 

 part of the middle lobe of the brain, and presents three particular 

 orifices, namely, the foramen rotundum, near it* anterior and inner 

 margin, through which the superior maxillary nerve passes from the 

 Oasserian ganglion of the fifth pair ; the foramen ovale, much larger 

 and near the posterior and inner border, through which the inferior 

 maxillary nerve goes from the same ganglion ; and the foramen 

 spinoeum, near the outer and posterior angle, which transmit* the 

 middle meningeal artery. This outer angle (b, 9), which fit* in between 

 the petrous and squamous part* of the temporal bone (see fig. 11), is 

 named the spinous process. The outer or temporal surface (a, 6) is 

 slightly hollowed, and forms part of the temporal fossa, rising up at 

 the lower part of the side of the skull as far a* the anterior inferior 

 angle of the parietal bone. At it* lower border it turn* abruptly 

 inwards at a alight ridge, below which it is continued to the pterygoid 

 processes--, and forms part of the zygomatic fossa ; it* posterior border 

 articulate* with the squamou*, it* anterior with the frontal bone. The 

 anterior or orbital surface (a, 7) is flat and smooth, and forms part of 

 the outer wall of the orbit, where it articulates with the malar, frontal, 

 and upper jaw bones. 



The Leuer Alie (4, 3, 8) are long, narrow, sharp-pointed processes 

 projecting horizontally outwards from the front and upper part of 

 the body. Internally and behind they bear the anterior clinoid pro- 

 cesses, beneath which are the opti foramina for transmitting the 

 ophthalmic arteries and the optic nerves from the commissure to the 

 orbit. The upper surface of these also is flat, and supports part of the 

 brain. The anterior border is articulated with the orbital plates of 

 the frontal bone on either side, and in the middle, where the ethmoidal 

 spine project*, with the ethmoid bone. The posterior border lies in 

 the Fissura Sylvii, between the anterior and middle lobes of the 

 brain. The under surface U smooth : between it and the anterior edge 

 of the great alx i* a gap, the foramen lacerum anterius, transmitting 

 nerves and a vein to the orbit 



The Pterygoid Processes (o, 4, 4) are directed downwards from the 

 under and outer part of the body. On each side there are two lamella}, 

 an external and an internal ; they are long and narrow quadrilateral 

 plate* nearly meeting in front, where they articulate with the palate 

 bone, and diverging behind no as to leave a space, in which the internal 

 pterygoid and circumflexus palati muscles are attached. The internal 

 and longer of the lamella; has at its lowest extremity a hook, the 

 Hamulnr process, round which, as on a pulley, the tendon of the last- 

 mentioned muscle pUys. At the upper part, where the pterygoid 

 proeesaes join the body, is a canal, the Vidion, running from before 

 backward* and transmitting the Vidian nerve. 



The Ethmoid Bone (fig. 11, /) is situated in the front and middle 

 pmrt of the base of the skull, between the orbits. Pig. 17 give* a 

 profile view of it from the left side. It presents six different aspects, 



Flf. 17. 



ad for the moiit part ia of a very light ipougy texture. It* upper 

 surface, which i presented to the brain, ha* in front and in it* middle 

 line a strong triangular proces*, the Cruta Oalli (l),to which the front 

 of the fall cerebri i* attached. The apex of this process i* directed 

 straight upward* ; the base is continuous below with the perpendi- 

 cular or nasal plate (2), which divides the ethmoid bone into two 

 equal lateral halves, and which, with the Vomer, which it join* below, 

 form* the greater part of the Septum of the nose. The Criata Qalli, 

 stooping downwards and backward*, u gradually lost behind, where the 

 Ethmoid bone receive* the spine of the sphenoid. On either side of it 

 i* a narrow quadrangular plate (the Cribriform Plate), on which the 

 bulb of one of the olfactory nerve* rests. Each i* perforated by a 

 number of holes through which the branches of the olfactory and 

 another smaller nerve pas* to the interior of the nose. In front, and 

 long part of the border of each plate, are the orifices of numerous 



cell*, which, in the entire skull, are closed in by the frontal bone and 

 U orbital plate*, and communicate with the frontal sinuses. 



The surface of the upper part of each side of the ethmoid bone U 

 brmed by a thin smooth quadrilateral plate, the orbital plate (3), 

 which forms great part of the inner wall of the orbit, and unites above 

 with the corresponding plate of the frontal (leaving two small aper- 

 lures, the anterior and posterior internal orbital foramina, for the 

 passage of small nerves and vessels), in front with the lachrymal, below 

 with the orbitar portions of the upper jaw and palate bones, and behind 

 with the sphenoid. Between the orbital and nasal plates, each half 

 of the bone is formed of cells and folds of very thin lamella), which 

 form part of the chambers of the nose, and have the olfactory mem- 

 brane and nerve* spread out upon them. [SMELL.] The principal 

 part* are the middle turbinated or spongy bone (4), a roll of thin bone, 

 which form* the lower border of the cell* ; and a smaller but similar 

 roll higher up, and confined to the back part, called the superior 

 turbinated or spongy bone (5). Under each roll at its posterior part 

 ia a passage to the cella,.called respectively the Superior and the Middle 

 Heatus of the nose. The ethmoidal cell* communicate in front with 

 the frontal, and behind with the sphenoidal cells or sinuses. 



The six bones just described inclose the Brain, forming a cavity 

 whose size, compared with that of the crania of brute*, is one of the 

 most distinguishing marks of the human specie*. [BBAIX.] 



The formation of the sutures seems to have the same end. The 

 outer table* of the exposed bones have their edges finely dovetailed, 

 and are thus so immoveably held together that none but a violently 

 expansive force exercised at once on the whole interior of the cavity 

 can separate them. The inner tables ore simply apposed with a very 

 thin intermediate layer of cartilage ; an arrangement which, as Sir 

 Charles Bell (who has written most ingeniously on this subject in his 

 ' Animal Mechanics'), says, U often imitated in works of art, in which 

 tough materials, such as wood, are joined by mutually fitting denta- 

 tion* ; and brittle ones, such as glass or marble, by smooth edge* and 

 a layer of cement A similar mode of opposition i* seen between all 

 the bones of the skull that are not exposed to direct violence. 



The top of the skull presents transversely an arched formed by the 

 two parietal bones (fig. 9), whose most prominent parts, like those of 

 the frontal, occipital, and others, are stronger and thicker than any 

 others ; a circumstance adapted for greater resistance to force, whether 

 applied directly against those parts, or to the summit of the arch, 

 from whence it would fall chiefly on them. The strength of this arch 

 is further secured by the lower parts of the parietal bones being held 

 in by the overlapping upper borders of the temporal and sphenoidal 

 bones, other parts of which, passing across the base of the skull, 

 hold the parietal bones, which by pressure from above might be mado 

 to start outwards or pushed inwards, as beams hold the walls of a 

 house from being driven either in or out by the weight of the roof. 

 Taking the whole upper part of the skull as a dome, the same strength 

 of resistance to superincumbent pressure is obtained at every part by 

 nearly similar means, especially at the coronal suture, where, as has 

 been already said, the parietal bones overlap the frontal at the support* 

 of it* arch, and are themselves overlapped by it at the summit of 

 their own. In this regard also may be noticed the strength and 

 thickness of the angular processes, and of the orbital arches extended 

 between them (fy. 11), which serve a* supports for the front of the 

 dome ; and the thickening of the bones along the course of the longi- 

 tudinal and lateral sinuses, resembling groins in masonry. 



The second chief division of the Skull include* the bones of the 

 Face, the principal of which are represented in fig. 9 and 18. 



The Nasal Bones (fyt. 9, 10 18, g) form the upper part of the bridge 

 of the nose. They are narrow and quadrilateral ; thick above, where 



Fig. 18. 



they fit into the nat.il notch of the frontal bone; brond and thin 

 below. The outer border of each articulates with that of the amending 

 process of the upper jaw-bone ; the inner in in contact with that of the 



