THE MAMMALIA— MAN AND BEASTS. 



33 



food to the mouth by means of hands, or of feet constructed somewhat similar to 

 hands, l^either do vre find it in the Elephant, where the proboscis is substituted for 

 hands nor is it to be foxind in the Cetacea, which obtain their food in water: the 

 latt°r possess the shortest necks of all the Mammaha. It appears singular that the 

 number of cervical vertebrae should remain constantly the same, although the necks 

 of different animals differ so very widely in length. In Man, we sometimes observe 

 the vertebrse of the back and loins to vary from their usual number, but never those 

 of the neck. 



The Dorsal Vertebrae are very large and long in all quadrupeds with long necks 

 and ponderous heads, especially in the Horse, Camel, Elephant, and Camelopard, 

 which arrangement seems necessary to afford a place of attachment for the Ug amentum 

 nuchce. 



The number of Lumbar Vertebrse varies exceedingly in different Mammaha; and 

 when the length of the body is remarkably great, it is usually occasioned by a greater 

 or less number of these vertebrae of the loins. Their motion is more or less restrained 

 in nearly all quadrupeds ; and this is effected by the exterior side of each posterior 

 articular process being directed backwards, so that the anterior articular process of the 

 next vertebra falls between two prominences. The shape of the body in animals, 

 whether slender, short, or thick, is chiefly determined by the length of the loins, and 

 this again depends upon the number of the lumbar vertebrae. 



The anterior ribs are attached in front by cartilaginous portions to a 

 sternum or breast-bone, composed of a certain number of vertical pieces. 



Some of the ribs are attached only by the hinder extremity to the spine, and arc 

 called _/a?se or shaking ribs, to distinguish them from the true, which are united to 

 the sternum. The ribs of the Mammalia vary greatly in number. In no instance is 

 the total number less than twelve, being the number in the human skeleton. The 

 horse has 18 ribs, being 8 true and 10 false; the Elephant has 20 ribs, being 7 truo 

 and 13 false. The strength of the spinal column, and its consequent ability to sustain 

 great weights, depend very much upon the size of the ribs, and upon the figure which 

 they give to the rest of the body; accordingly, we find that in the large herbivorous 

 quadrupeds, which are usually employed as beasts of burthen, the ribs are thick and 

 broad. Those quadrupeds which have no clavicles have less curvature upon their 

 sides than the others. Being never required to use the anterior extremity as a pre- 

 hensile member, the chest is narrowed and flattened upon the sides, especially towards 

 the sternum, whereas Mammalia with clavicles have their chest shaped nearer to the 

 human form. 



The ribs are remarkably strong and compactly set in all quadrupeds destined to 

 roll themselves up when attacked by other animals. In all Mammalia, they have only 

 a very limited motion upwards and downwai'ds, and their articulations are strengthened 

 by a groat number of ligaments. There are capsules at each articulated extremity of 

 the ribs, which retain them upon the bodies and transverse processes of the vertebra. 

 They are further secured by means of two ligaments, the one being inserted into the 

 transverse process of the superior vertebra on the inxide, and the other into the lower 

 articulating projection of the same vertebra, but on the outside. By this means the 

 cavity of the chest is rendered secure, as well as by the capsule which unites tlie 

 otlier extremity to the prolonged cartilage of the breast. There is also a ligamentous 

 expansion between the ribs, connecting the lower edge of the one rib to the upper 

 edge of the next. 



In all animals, excepting perhaps the Marmot, the thorax or chest is narrower than 

 in Man, and deeper from the spine to the breast. This peculiarity arises from the 

 greater length of their breast-bone, and the less-marked flexure of their ribs. The 

 Camelopard, and other animals having very long legs, possess the keel-like form of 

 the chest in a remarkable degree; this is especially observable in the Deer tribe. 



The Sternum, or Breast bone, differs generally from that of man, in being composed 

 of a greater number of pieces, and in being rounder and narrower. It is also longer 

 in proportion to the rest of the body. In the Mole, the sternum is remarkably thick 

 and strong. To enable this animal to excavate the earth for the admission of its 

 body, the anterior portion of the clavicle is compressed upon the sides, so as to give it 

 the form of a ploughshare. It projects beyond the hne of the first rib, and thus 

 enables the animal to burrow with singular rapidity. 



The anterior extremity of the Mammalia commences in a shoulder-blade, 

 which is not articulated, but merel}' suspended in the flesh; often resting 

 on the sternum, by means of an intermediate bone, called a clavicle. 



The anterior extremities, or fore-limbs, often appear to differ widely from each other 

 upon superficially comparing the external forms in different species with each other 

 and with I\Ian; thus, the Dolphin and Whale seem to possess fins, ana the Bat wings. 

 But this difference is more apparent than real. Upon examining their internal struc- 

 ture, we find that the fore-limb consists always of four component parts, the Scapula 

 or shoulder, the Humerxis or arm, the Fore- Arm, and the Hand. In the fins of the 

 Cetacea we perceive all these bones flattened in their form, and scarcely capable of 

 moving upon each other, while the wing of the Bat is really a hand, with its fingers 

 excessively elongated. There are also found a class'^of limbs intermediate bet'.veen 

 the fore-foot of the quadruped and the pectoral fins of the Cetacea. The Otter, Seal, 

 and Walrus, have their bones covered with a web-Uke integument, adapted for the 

 purpose of swimming. Their limbs are much more freely developed than in the Ce- 

 tacea, and possess a greater freedom of motion, so that they form an intermediate 

 transition from the one structure to the other. 



The Scapula, or shoulder-blade, is found in all Mammalia. In general, the edge 

 of this bone, next to the spine, is rounded, and the posterior angle is thus rendered 

 blunt. The shape of the Scapula depends on the presence or absence of a clavicle; 

 the acromion not being so prominent when this clavicle is absent ; and then there is 

 another process called the recurrent process, pointing backwards almost perpendicularly 

 to the spine. The posterior angle is also most elongated in those species having com- 

 plicated motions of the anterior limbs. In animals having only the rudiments of 

 fclavicles, or none, the acromion process is nearly deficient. 



The Clavicle, or Collar-bone, is not found in species which employ their anterior 

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limbs only for progressive motion. In the Mole, the clavicle is of an extraordinary thick- 

 ness, being nearly square, and slightly greater in breadth than in length. In the Bat, 

 it is very large and strong. Indeed the Clavicle is found in all Mammalia which use 

 their fore-limbs for burrowing, hke the jMole; for raking the ground, like the Hedge- 

 hog and Ant-eater ; for climbing, like the Sloth ; or for holding objects, like the 

 Beaver and Squirrel. In the other Mammalia, we often find in its place a smaller 

 bone called the Os claviculare, analogous to the true clavicle, but merely connected 

 to the muscles. This arrangement is observed in most Carnassiers, and in many 

 Rodentia. 



Sir Charles Bell observes, that " Animals which fly, or dig, or climb, as bats, moles, 

 porcupines, squirrels, ant-eaters, r.rmadilloes, and sloths, have the clavicle ; for in them 

 a lateral or outward motion is required. There is also a certain degree of freedom in 

 the anterior extremity of the cat, dog, marten, and bear; they strike with the paw, 

 and rotate the wrist more or less extensively ; and they have therefore a clavicle, 

 though an imperfect one. In some of these, even in the Lion, the bone which has the 

 place of the clavicle is very imperfect indeed; and if attached to the shoulder, it does 

 not extend to the sternum, it is concealed in the flesh, and is like the mere rudiments 

 of the bone. But however imperfect, it marks a correspondence in the bones of the 

 shoulder to those of the arm and paw, and the extent of motion enjoyed. When the 

 Bear stands up, we perceive by his ungainly attitude and the motion of his paws, that 

 there must be a wide difference in the bones of his upper extremity from those of the 

 Ruminant or Sohpede. He can take the keeper's hat from his head and liold it; he 

 can hug an animal to death. The Ant-bear especially, as he is deficient in teeth, 

 possesses extraordinary powers of hugging with his great paws: and, although harm- 

 less in disposition, he can squeeze his enemy, the Jaguar, to death. These actions, and 

 the power of climbing, result from the structure of the shoulder, or from possessmg a 

 collai--bone, however imperfect. Although the clavicle is perreet m man, thereby 

 corresponding with the extent and freedom of the motion of his hand, it is strongest 

 and longest, comparatively, in the animals which dig or fly, as in the Mole and the Bat." 



It follows from these observations, that animals possessing a clavicle, and thus having 

 the power of hugging, are unable to bear a severe shock on their fore-limbs without 

 running the risk of fracturing the collar-bone. " If we observe the bones of the 

 anterior extremity of the horse," continues the same eminent anatomist, ** we shall 

 see that the scapula is obUque to the chest ; the humerus oblique to the scapula; and 

 the bones of the fore-arm at an angle with the humerus. AVcrc these bones connected 

 together in a straight line, end to end, the shock of alighting would be conveved throuf^h 

 a solid column, and the bones of the foot, or the joints, would suffer from the con- 

 cussion. \Mien the rider is thrown forwards on his hands, and more certainly when 

 he is pitched on his shoulder, the collar-bone is broken, because in man this bone 

 forms a hnk of connection between the shoulder and the trunk, so as to receive the 

 whole shock ; and the same would happen in the horse, the stag, and all quadi-upeds 

 of great strength and swiftness, were not the scapula; sustained by muscles, and not by 

 bone, and did not the bones recoil and fold up." 



The varieties of form observed in the clavicles are very great. In the Two-toed 

 Sloth they have the form of a rib; in the Jlole they are nearly cubical. The cla- 

 vicles arc very long in the Bat, but in the Quadrumana they gi-eatly resemble the 

 same bone in Man. The clavicle is not found in the Cetacea, Ruminantia, or Soli- 

 peda, and generally it is deficient in all long-legged quadrupeds, having a keel-shaped 

 chest. 



The anterior extremity of the Mammalia is continued by an arm, a 

 fore-arm, and a hand. 



The Arm-bone, or Humerus, varies considerably in the elevation of its processes, and 

 in its length and breadth. In quadrupeds, the Humerus is much shorter compara- 

 tively than in the human subject. It was this circumstance which has led the ancient 

 anatomists, and persons ignorant of Comparative Anatomy, to consider quadrupeds as 

 having the elbow turned forwards. That part which is usually considered the knee 

 of a Horse, corresponds to the human wrist, the arm-bone being concealed within the 

 muscles of the shoulder. The Humerus is very long in the Bat, but very short and 

 thick in the Jlole. 



The human fore-arm is composed of two distinct bones, the Ulna and the Radius ; 

 the former swings with a hinge-like motion upon the elbow, and the latter gives the 

 wrist and hand a rotatory motion. Accordingly, in all animals which use their fore- 

 arms, hke Man, for other purposes than walking, both of these bones are distinctly 

 developed; but, in the true quadrupeds the Ulna diminishes in size, is altogether 

 absent, or becomes a mere appendage to the Radius, which is then the principal bone 

 of the fore-arm. In cattle, the Ulna is immoveably united to the Radius throughout its 

 entire length, becomes finally ossified, and may then be considered but as a single bone. 

 They thus form a perfect hinge-hke joint, which does not admit of any rotatory motion, 

 and having the pulley placed on the end of the Humerus. These quadrupeds have 

 therefore their anterior extremities always in a state of pronation, that is, the back of 

 the wrist is always turned upwards. 



The general arrangement of the bones in the anterior limbs, though the same 

 throughout the entire class, yet changes surprisingly in its details with the different 

 orders and genera. In the Bat the radius is nearly deficient, being reduced merely 

 to a slender and sharp-pointed rudiment. Its thumb is short, and furnished with 

 a hooked nail, while the phalanges of the four fingers have no nails, but are extremely 

 long and thin, almost like the spines of a fish, while the membraneous, or wing-like 

 expansion, is extended upon them. Again, in the Mole, we see a striking difference 

 in the form of the anterior extremity. The bone of its fore-arm is thin in the middle, 

 but surprisingly expanded at either extremity; and a peculiar bone, called the faLci- 

 form bone, is found at the extremity of the radius. Its paw is shaped like a shovel, 

 the phalanges of the fin^^ers are supphed with sesamoid bo'nos and numerous processes, 

 which increase the angle of insertion for the tendons, and facilitate the great muscu- 

 lar motion required by this httle animal. The Flying Squirrel possesses a peculiar 

 aiTangf;ment for enabling it to spring from great heights. This consists in a sharp- 

 pointed bone at the outer edge oj' its Wrist, connected to that part by means of two 

 smaller round bones. 



