HOG 



MA M M A L I A. 



.the bones in the human leg are as follows: one 

 in the thigh as already mentioned ; one on the 

 knee, the knee pan, which is embedded in the ten- 

 dons, and serves to keep the joint steady, and also to 

 protect those tendons from injury when the knee is 

 very much bent, and to prevent it from bending in 

 the contrary direction, and yet leave it more flexible 

 than it would be if its motion were stopped by bone, 

 and fatigue it less than if it were held back merely by 

 soft matter. After these, the leg itself contains two 

 bones ; he tarsus, or ankle arid heel taken together, 

 consists of seven bones ; the metatarsus, of the same 

 number as the metacarpus ; and the toes, also of the 



- same number as the fingers and the thumb, the great, 

 toe having only two phalanges as the thumb has, and 

 each of the smaller toes three. Thus the whole ske- 

 leton may be said to contain two hundred and forty 

 bones, besides those which, as we have remarked, may 

 be regarded as made up of, or divided into parts. 

 We shall now introduce a figure of the skeleton, 



and proceed to make such general remarks upon it as 

 may prepare us for understanding how the different 

 bones are united together in their natural arrange- 

 ment, and in what manner they are worked by the 

 muscles ; and this comprises the whole mechanics of 

 the body, and furnishes us with a standard whereby to 

 estimate the general mechanics of the mammalia. 



We shall glance very briefly at the bones composing 

 the several parts in their order ; and though our figure 

 is a mere sketch or simple index, and we have not 

 confused it by references, yet any one may, by means 

 of it, and his own body, easily make out the positions 

 and general forms of the principal bones, which is at 

 all events a beginning. 



Bones of the Head, The fronfal bone, which is a 



very characteristic one in the human subject, forms 

 the forepart of the skull, and the upper arches of the 

 orbits of the eyes. It has various elevations on its 

 external surface, is perforated in its substance by the 

 frontal sinuses, and has some spinous processes on the 

 inner surface, which serve to keep the brain steady in 

 its cavity. The ridges and inequalities on this, and 

 on all the bones, are far more conspicuous in the male 

 subject than in the female. 



The parietal bones, or walls of the skull, compose 

 the upper part behind the frontal and the sides ; and 

 they have not any very remarkable projections from 

 their surfaces, neither are they perforated for the 

 admission of any important organ ; but there is a hole 

 in each, near the corner at which it joins the frontal 

 bone and the temporals. 



The temporal bones form the lower parts of the 

 sides of the head, and may be said to contain chiefly 

 the organs of hearing. They also have various pro- 

 cesses on their surface, and are pierced with holes for 

 the passage of arteries and veins. 



The occipital bone forms the back of the head, 

 and it is the bone by means of which the head is arti- 

 culated on the spinal column, and also that through 

 which the spinal continuation of the brain finds its 

 passage into the tube or cavity which all the vertebrae 

 contain for its reception. The joint here is a hinge 

 joint, having the plane of its action parallel to the 

 mesial plane. It is double, there being two condyles, 

 or knobs on the lower part of the bone of the skull, 

 and two cavities in the upper side of the vertebrae, on 

 which they work. This gives protection to the 

 spinal marrow, and also allows the head a very con- 

 siderable range for motion backwards and forwajds ; 

 but this is not the joint upon which the lateral and 

 twisting motions of the head are performed. This is 

 the joint, however, that gives the principal motion to 

 the head in the direction of the mesial plane, and the 

 one upon w.hich the head is balanced ; and so well 

 is it adapted to the keeping of the balance, that the 

 condyles of the occipital bone are, on the average, 

 immediately below the centre of gravity of the skull 

 and its contents. 



The sphenoid, or wedge-shaped bone, forms the 

 base of the skull. It has many processes and irre- 

 gularities on its internal surface, by means of which 

 it keeps the brain upon a very firm base. It is per- 

 forated by the two openings by which the eyes arc 

 connected with the internal cavity of the skull. 



The ethmoid bone is situated at the back of the 

 nose, and unites the proper bones of the nose to the 

 frontal bone. The bony plate of the nose stands out 

 from it ; and its cavities, from which it gets its name, 

 which means that it is like a sieve, are the chief 

 receptacles of the organs of smell The frontal 

 bones of the nose are the nasal bones, which form the 

 firm part at its union with the frontal bone ; and they 

 are pierced so as to admit the matter of tears gene- 

 rally into the cavity of the nose, though these last 

 are, more strictly speaking, bones external of the 

 nose, or rather between it and the inner parts of the 

 orbits of the eyes. They are the ungual bones. 



The cheek bones are situated below the eyes and 

 support the cheeks. They have various processes and 

 cavities, and their form gives considerable character 

 to the head. 



The upper jaw bones contain the sockets of the 

 upper teeth, and also form a considerable portion of 

 the palate, and serve to continue the organs of smell 



