MAMMALIA. 



107 



o the mouth, where there is so curious a sympathy 

 ictween. them and the organs of smelling. The bones 

 if the palate, properly so called, are situated in the 

 lind part of the palate, and between the cavity of the 

 nouth and the nasal openings. 



The vomer, or ploughshare bone, stands out from 

 he ethmoid, and forms the principal part of the sep- 

 um, or partition which separates the nostrils from 

 ach other ; and this is prolonged in the cartilaginous 

 art of the septum, as the sides of the cavity are by 

 heir cartilages. 



None of the bones that have hitherto been men- 

 ioned have any proper articulations upon each other. 

 Phey support the brain, and the principal organs of 

 he senses, as well as afford the plane of resistance 

 gainst which the lower jaw acts in preparing the 

 uod for the stomach, and they also give assistance 

 o the muscles which move the jaws and the eyes, 

 nd give all the varied expressions to the face; but 

 tone of these can be said to be subject to any of 

 he mechanical actions of the animal. The other 

 irincipal bone of the head is different. That is, 



The lower jaw, which has both a vertical or open- 

 ng and shutting motion, and a lateral rolling or grind- 

 ng one ; and all mammalia which have this last 

 notion of the lower jaw, are capable, in part at least, 

 I' subsisting upon vegetable food, whereas there is 

 o such motion in animals which kill and eat other 

 nimals. 



The teeth, when complete, are thirty- two, eight 

 n each side of each jaw- Eight of these are incisors, 

 aur canines, and the remainder grinders, equally dis- 

 ributed in both jaws. The incisors have only one 

 utting edge, and a single fang or root ; but the 

 ;rinders have double flattened crowns, and each of 

 hem has two roots. They are not, however, so 

 lecidedlv grinding teeth as those of the animals which 

 eed solely upon vegetable matter. In these, the 

 namel, or harder part, is dispersed in ridges or layers, 

 Iteriiatiiig with the bone ; but in the human grinders 

 he enamel covers the whole crown of the tooth. 



We shall mention some of the leading forms both 

 if the partial and the more complete motion of one 

 ione upon another, when we come to treat of those 

 arts of the skeleton in which such articulations 

 iccur ; but as the bones of the head form one of the 

 iest instances of the union in which there is no motion, 

 t may be proper to notice them here. 



The general technical name given to this kind of 

 inion between bones is synarthros'is, which implies 

 hat they are equally related in the junction, or that 

 icither of them moves upon the other. The union, j 

 ir line of union, is called a suture or seam ; and it is 

 listinguished as serrated, or toothed when the bones 

 re indented into each other. This is by far the 

 irmest kind of suture, and we accordingly lind it at | 

 he union of the most important bones the frontal, ' 

 >arietal, and occipital bones of the skull, and the 

 iheek bones. This kind of suture is very difficult , 

 :ither to be separated or displaced. The second kind 

 if suture is that in which the edges of the bones are 

 nerely brought together, without any toothing or 

 nterlocking. This is a feeble kind of union, as corn- 

 tared with the former, and therefore it. occurs between 

 uch bones as those of the nose and the two parts of 

 he upper jaw, upon the union of which there is little 

 train. The third kind is called squamous or scaly, 

 ircai! -c the edge of the one bone is thin and over- 

 aps that of the other. The temporal bones form this 



sort of suture with the occipital, which they overlap 

 at the junction. From its form, this suture is more 

 yielding to a strain than the others are. 



All the three forms, however, yield more than if 

 they were a solid bone, and when a fracture of the 

 bone does happen, it is not propagated beyond the 

 suture. All these contrivances render the skull much 

 stronger with the same quantity of materials, than it 

 could have been rendered by any other means ; and 

 as in man. the upright position supports it nearly 

 upon the centre of gravity, it is borne in the easiest 

 possible manner upon a column, which is so finely 

 adapted for supporting it. 



Bones of the Trunk. As the skull is the chief 

 bone of the head, and contains the brain, so the spine 

 is the most important bone in the trunk, and contains 

 the continuation of the same mass. The spine, in the 

 balancing of the body in all the varied attitudes which 

 are necessary in the human subject, requires to be 

 firm, and at the same time flexible to a considerable 

 extent ; and as injuries to the contents .of this spine 

 are of the most fatal nature, it is necessary that, in all 

 its motions, it should be protected against disloca- 

 tion. This is accomplished by the numerous pro- 

 cesses with which the vertebrae are beset, and by the 

 mode of their union, and the nature of the substance 

 that unites them. The processes of the spine are 

 so arranged, that it i not very easy to dislocate a 

 spine without breaking some part of it. The muscles 

 which give it its motions have comparatively little 

 or no power upon the joints, and the matter with 

 which these are connected is very tousjh and elastic. 

 All the different parts of it have different kinds of 

 motion. In the neck, the lateral motion across the 

 mesial plane is nearly as great as that in the plane ; 

 but in the dorsal vertebrae, where the ribs are attached, 

 and where their order would be deranged, and the 

 contents of the chest disturbed by a great extent of 

 lateral flexure, the cross motion is more limited. 

 There is a contrary flexure in the spine, which is at 

 once graceful and contributes to the strength of the 

 organ. The upper extremity inclines forward, so as 

 to reach the central part of the bone of the skull, and 

 this at the same time affords room for those muscles 

 and their tendons, which communicate the principal 

 motions to the head. The spinous processes in the 

 upper part are short ; and it is not till we come to 

 the setting on of the neck, as it is usually called, that 

 we can feel a prominent process through the skin. 

 They are more produced in the dorsal vertebrae, and 

 they are far more produced in running mammalia, 

 which require a firmer lateral support to their blade- 

 bones than is necessary in man. 



The projecting parts of the vertebree of the spine, 

 and their perforations may be briefly stated as fol- 

 lows : The first vertebra of the neck, which imme- 

 diately supports the condyles of the occipital bone 

 has two transverse processes, two articulating ones, 

 and two inferior oblique ones. This vertebra is 

 styled the atlas. The second vertebra is called 

 toothed (dentata). It has two transverse and four 

 oblique processes ; and the articulation is a cleft tooth- 

 like process, which acts in the cavity of the atlas, and 

 admits of the lateral and twisting motions of the 

 head. The remaining five of the neck resemble the 

 second one in other respects ; but they have not the 

 toothed process. All these have the central opening 

 for the spinal marrow, und two lateral holes in each. 



The vertebras of the back and luins have the same 



