THE MAMMALIA— MAN AND BEASTS. 



31 



ence in the organs by which their movements are efFeeted; and, consequently, the 

 skeletons exhibit many important peculiarities when compared with those of Man, and 

 with each other. Yet, whatever differences may be found to prevail, one general 

 character can be discovered throughout the whole. The same bones which compose 

 the arm and hand of Man, or of the Monkey tribe, are found equally in those genera 

 which use their fore extremities for walking, swimming, or flying ; the proportions of 

 the bones bein"- only altered, or some of the parts being obhterated, or changed. We 

 find them equally in the fore-leg of the Deer, in the wing of the Bat, and in the fin 

 of the Whale. One order of animals having an abdominal pouch for containing the 

 young, are suppUed with two additional bones, called marsupial^ moved by appropriate 

 muscles. 



The interior composition in the bones of the Mammalia is generally the same; but 

 their texture varies, being denser and closer in the smaller tribes, but very fibrous, 

 and loosely arranged in the Cetacea. The texture of the bones in the sea-beasts 

 is particularly adapted for locomotion in water, being aided by the hghtness of their 

 structure, and by having all the cells of their bones filled with an oily fluid. 



The joints or articulations by which the bones of the Mammalia are connected to- 

 gether greatly influence the habits and general economy of these animals. Some of the 

 joints are only capable of performing an imperfect motion, while a greater latitude is 

 assigned to others. Appropriate names have been assigned to these several kinds of 

 articulations, and they have been further arranged in divisions and sub-divisions. 

 Some kinds of articulation are observed to be altogether peculiar to certain classes of 

 Mammaha; while it frequently occurs that the corresponding bones will vary in their 

 mode of articulation for dift'erent Mammalia. Other bones again, which aie separated 

 in one genus, will be intimately and closely united together in another. 



The first class of articulation (Diarthrosis) contains the free and perfect joint. 

 The opposite sm-faces of the bones are distinct and well defined, being covered with 

 a polished and smooth cartilage. A continuation of the periosteum or external cover- 

 ing of each bone passes onwards from one to the other, forming a kind of capsule, or 

 httle bag, and permitting nothing either to pass within or to escape from the cavity. 

 But the periosteum does not cover the articular cartilages, it merely forms the exter- 

 nal covering of the entire joint. Other ligaments frequently strengthen this covering 

 either externally or within the capsule, and thus will limit the motions of the bones 

 more perfectly than the capsule alone could have done. The interval within the cap- 

 sule is occupied by an oily fluid, or else each bone is covered by a smooth and polished 

 cartilage. Sometimes a piece of cartilage will be found ; perhaps also some peculiar 

 gland, or other soUd body. 



The direction and extent of motion possessed by the bones of the Mammalia is 

 dependent upon the rigidity or number of the hgaments, as well as upon the form and 

 depressions found in the articulated surfaces. 



When a bone is articulated to another by one of its extremities, it admits only of 

 two species ot motion, torsion or flexion. 



The torsion, or twisting, takes place when the bone is capable of moving round its 

 own axis, or else round an imaginary axis passing through the articulation. This 

 kind of motion can only be found when the articulated surfaces are plain or spherical, 

 and the latter are alone capable of motion in every direction. Flexion or bending 

 takes place when the extremity of the bone, farthest from the joint, approaches the 

 bone which is fixed. 



The different kinds of torsion have been assigned different names ; there is the 

 hinge-joint (Ginglimus)^ the ball and socket-joint (EnarthrosU or Arthrodia), and 

 the rotating joint (Trochoides). 



The manner in which the head is attached to the trunk, the lower jaw to the head, 

 and the several parts of the Umbs to each other, differs in the several classes of ani- 

 mals. The head of the Mammalia is united by a hinge-joint to the neck; in the 

 Birds it is connected by a ball and socket-joint. Even among the Mammaha them- 

 selves the ai-ticulations ai*e found to differ. In Man, the radius of the fore-arm is con- 

 nected by a ball and socket-joint with the humerus, at its one extremity, and it rotates 

 upon the other. But in the Rodentia, and many Pachydermata, the radius is con- 

 nected by a hinge-joint with the humerus, and is immoveable at its other extremity. 

 In some species these bones are even completely united. 



The second class of articulation (Synarthrosis) admits of no motion whatever; it 

 is said to form a suture when two flat bones join each other by the edges; to bo squa- 

 mous, when the thin edge of the one bone covers that of the other; denticular^ when 

 the edges are notched and indented together ; and harmonic, when they simply touch 

 each other. We find, in the bones of the face and head of IMan, instances of these 

 different kinds of articulation. The manner in which the bones of the skulls belong- 

 ing to the several IMammalia ai'e joined together, bears a great resemblance to that 

 observable in Man; and we find, in all, that they have a tendency to ossify as their 

 ages increase. A variety of this kind of articulation is found in the teeth of Man 

 and Quadrupeds. These are inserted hke wedges into the cavities of other bones. 

 To this style of connexion the name of Gomphosis has been assigned. 



There is no instance found in the human skeleton corresponding to that singular 

 kind of articulation observed in the nails of the Cats. These are inserted into small 

 cavities in the last phalanges of the toes, and at the same time they receive a pivot, or 

 eminence of the phalanx, into a small cavity of their own, prepared to receive it. This 

 curious contrivance is also found in other quadrupeds with powerful claws. We also 

 find it in the task of the Morse, where a small pivot is observed to project from the 

 basis of the alveoli. 



The third kind of articulation (AmpkiarthrosisJ admits only of a slight and re- 

 stricted motion. This is not occasioned by the form of the bones, which are perhaps 

 perfectly adapted for free motion, but by the cartilages and ligaments which are placed 

 between the bones forming the articulations, and uniting fii-mly with them. The ver- 

 tebrae of the back exhibit this restricted motion; but the bones of the pelvis are 

 joined in such a manner as scarcely to permit any motion whatever. The bones of 

 the vrrist and instep are considered, by some anatomists, to belong to this class ; for, 

 though they appear to be provided with a few smooth articulated surfaces, yet they 

 are confined so greatly by the sirrounding ligaments, that they move upon each other 

 with great difficulty and through a very narrow space. 



In the second and third kinds of articulation, the edges or surfaces of the bones 

 either come immediately into contact, or else they are bound together by a substance 

 which attaches itself throughout their entire parts of connexion. Also, the perios- 

 teum is continued from one bone to the other, and is more intimately connected at 

 the place of their junction than at any other part. In this respect they differ wholly 

 from the kind first described. 



The muscles which set these bones into motion are as various as the movements 

 destined to be performed. Those composing the trunk of the Elephant are unrivalled 

 for the union of strength, variety, and delicacy. As the snout of most animals is 

 incapable of performing any considerable motion, we are naturally struck with asto- 

 nishment at seeing an organ, which appears at first sight to be merely a prolon'ration 

 of the snout, performing all the offices of the human hand. This delicacy is owing 

 to the immense number of minute muscles which are arranged in vai'ious directions 

 and thus enable the animal to execute the various movements of the organ. Upon mak- 

 ing a transverse section of the proboscis, counting the number of short muscles, and 

 then allowing the breadth of a hne for the succeeding ones, which is considerably 

 more than their thickness, some estimate may be formed of the number of muscles 

 composing the trunk of the Elephant; and, upon adding these to the number of 

 bundles comprising the horizontal layers, they are found to amount to between thirty 

 and forty thousand. The snout of the Tapir is formed on a similar principle, with an 

 additional muscle, corresponding to that which raises the upper hp of the horse. 



In Monkeys, the muscle which frowns (corrngator supercilii} is large, and is fre- 

 quently used, but without expressing the feelings indicated by that action in Man. In 

 most quadrupeds the muscles, moving the external ear, are more strongly developed 

 than in Man. They are thus enabled to give a great variety of attitudes to that organ, 

 which enables them to collect sounds in every direction. Most quadrupeds, after an 

 agreeable sensation, will erect their ears, and depress them when displeased, in the 

 same manner as the Horse is in the habit of doing. Those animals which possess the 

 power of rolling themselves up, as the Hedgehog, have a number of curious muscles 

 for that purpose. The muscles of the tail are generally strongly developed; especially 

 in the Kangaroos, which use them for standing and leaping, and in the Monkeys hav- 

 ing prehensile tails. 



A certain degree of similarity prevails between the muscles of Man and those of 

 all the other IMammalia ; but this resemblance is, upon the whole, greatest between 

 Man and the Quadrumana. But we cannot fail to remark the small development iu 

 the calf of the log, and in the buttock, among the Apes, as these muscles are inti- 

 mately connected with the upright posture peculiar to I\Ian, and the beauty of the 

 human form. Many muscles, however, are found exclusively in Quadrupeds. Thus 

 the fleshy panniclo (payiniculus carnosusj, that sub-cutaneous covering of the body, 

 is of very great size in the Hedgehog, Armadillo, Porcupine, and all animals possess- 

 ing the power of rolling themselves up. This cutaneous expansion is even found in 

 the Cetaceous tribes; and the inhabitants of the Aluntian Islands are said to fabricate 

 a thread of great delicacy from the tendinous fibres of this muscle, procured from the 

 WTiale. 



Certain muscles are distinguished for their very great strength. Thus the Horse 

 i-: enabled to kick backwards with very great force, owing to the great development 

 of the Gluteus medius and Gemellus muscles. The Mole is enabled to burrow under 

 ground, and to throw up the earth, by the great magnitude of the pectoralis major^ 

 iatissimus dorsi^ and teres major muscles. 



There is also a curious arrangement in the muscles belonging to the epiglottis of 

 the several Mammalia. In the motion by which wc elevate and depress the hyoid 

 bone and the larynx, the muscles acting on the bones, and other hard parts, may be 

 compared to ropes drawing a resisting object in a certain direction. Innumerable 

 muscles of a complicated form may be seen in the tails of these Apes having that 

 organ prehensile. It is said that no less than two hundred and eighty muscles were 

 tliscovered by Mery in the prehensile tail of a Cercopithecus. 



Although the manner in which the bones are articulated determines the motions 

 which they ai"e capable of performing, yet it is by the number and direction of the 

 muscles attached to the bones that the motions performed by each bone are fixed. 



The muscles are attached to the bones by tendons. The fibres of which the ten- 

 don is composed are of a closer and denser texture than those of the muscles, and of 

 a silvery whiteness. Being penetrated by fewer vessels and no nerves, its substance 

 seems altogether gelatinous. It possesses neither irritability nor sensibility, and forms 

 the passive link, by means of which the muscle acts upon the bone. Portions of 

 tendon are found both inside and on the surface of several muscles; and even those 

 tendons, by which the muscles are inserted to the bones, penetrate a certain length 

 into their fleshy substance, where they are interlaced in various manners. The term 

 aponeurosis has been appUed to those tendons which are broad and thin. The ten- 

 dons have a great affinity for phosphate of lime, which they often absorb with facility 

 when their action is frequently repeated, and when employed to execute violent mo- 

 tions. This frequently occurs with the Jerboas and other animals, which constantly 

 leap with then- hinder Ihnbs. It is considered probable that all the elementary muscles 

 exercise an equal force at the moment of their contraction; but the degree of force 

 with which a muscle can be exercised greatly depends upon the manner in which its 

 fibres are disposed, and the situation of the muscle itself, in respect to the bone or 

 part it has to move. We therefore cannot estimate the force of a muscle by its mass, 

 or by the number of fibres of which it is composed, but must also consider the com- 

 position of the muscle and the method of its insertion. 



The muscles arc either simple or compound. In the simple muscles all the fibres 

 have the same disposition. The most usual are the ventriform, having all the fibres 

 nearly pai-allel, and forming a long bundle of a round form. The fleshy parts swell in the 

 middle, forming the belly of the muscle, and becoming smaller at each extremity, 

 where they terminate in tendons. Another kind of simple muscle consists of those 

 that are flat, and have parallel fibres, forming a sort of fleshy membrane, which is 

 terminated by aponeuroses or tendinous membranes, instead of ending in small teu- 

 dons. Both these kinds sometimes have tendons or aponeuroses in their middle, or 

 in other points of their bodies. It is obvious that, in either, the total action of the 

 muscle is equal to the sura of all the particular actions of the fibres; and that, if the 



