Sept. 25, 1879] 



NATURE 



509 



TAILS 1 

 'XXT'HAT are tails ? The question seems an almost trivia^ 



*' one in its simplicity. Dictionaries tell us that the 

 word " tail " denotes certain parts of animals, and also 

 the hindermost or lowermost portion of anything. We 

 speak habitually of the " tail of a coat," the " tail end of 

 a crowd," the "tail of a kite," and of "pig-tails," as well 

 as "tails of pigs." Evidently all these appellations are 

 in use from the perception of more or less close analogies 

 between the various things thus spoken of and certain 

 things which every one who speaks English must call a 

 tail — something which is unmistakably, truly, and properly 

 a tail. 



Such a thing, for example, is the tail of a cat or of a dog. 



Let us, then, examine such an object and see what a 

 typical tail is, and afterwards compare therewith other 

 structures more or less closely or remotely resembUng it. 



But in order to understand that part of a cat which is 

 called its " tail," we must understand those other parts 

 which are not its tail, since we can never know any one 

 thing whatever except by knowing other things from 

 which such one thing is distinguished. We could not 

 know " white," if everything that we saw was always of 

 that colour. 



The frame of a cat consists of a head, a trunk, limbs, 

 and a tail. 



Let us first look at its trunk. It consists of a solid 

 fleshy wall (partly strengthened by bones— the ribs, 

 breastbone and backbone) containing a cavity within ; 

 this_ cavity within the trunk is called the body-cavity. 

 Inside this body-cavity are a variety of parts (viscera), 

 such as the heart and its great blood-vessels, the liver, &c., 

 and the cavity is traversed by a long, much-coiled tube 

 called the alimentary canal, i.e., swallow, stomach, intes- 

 tines, &c.). Passing along the upper or dorsal side of 

 the body is the backbone just mentioned. This consists 

 of a complex chain of neatly articulated bones, each of 

 which is called a vertebra, and the whole series of such 

 bones form the vertebral column, spine, or spinal cobunn, 

 which are other names for the backbone. Now observe : 

 Each vertebra of the trunk is in the form of an irregular 

 ring. Therefore, as these rings come naturally in a series 

 one behind the other, they together form a canal. This 

 canal is called the neural canal, because it contains the 

 central part of the nervous system, or neural axis, also 

 improperly called the spinal marrow. 



Thus, altogether, the cat's trunk consists of a solid 

 case containing a body-cavity (within which lie the 

 viscera), while the dorsal region of the case is traversed 

 by the backbone or vertebral column, forming a canal 

 along which runs the spinal marrow. 



The neck is but the anterior prolongation of the trunk. 



The cat's head is much more bony in proportion than 

 is the trunk, and consists partly of a solid box, which 

 holds the brain and shelters the ears and eyes and partly 

 of a face and jaws, which latter bound the mouth. The 

 brain case has a large hole behind, which matches with 

 those which exist in each trunk vertebra, and through 

 this hole the neural canal is continued on into the hollow 

 of the skull, which is its expanded front end. Thus, 

 altogether, the cat's head is in certain respects like its 

 trunk. It IS traversed by the alimentary tube, which 

 opens at the mouth, and it has its dorsal part formed by 

 the much-expanded neural canal (the skull-cavity) which 

 contains the brain, or much-expanded anterior end of the 

 neural axis. 



The cat's limbs are very different in structure from the 

 head and trunk. No body-cavity is contained in them, 

 nor does the body-cavity of the trunk extend into any 

 limb, nor again is any limb traversed by any part of the 

 alimentary canal. Each limb has a solid bony support 

 within it, but this support (the skeleton of each limb) is 



' A Davis lecture recently delivered at ihe Zoological Gardens bv Prof 

 St. George Mivart, F.R.S.. V.P.Z.S. 



no part of the vertebral column, nor is it composed of 

 any sort of vertebras, but consists of a definite number of 

 longer or shorter bones which are related to the support 

 of the body or to its progression in walking, running, 

 jumping, &c. These limb-bones do not contain any 

 canal (as the backbone does), nor do they shelter any 

 continuation sideways from the central part of the nervous 

 system. 



We nowTcome'to the tail, and if we examine it, we 

 shall see that, to a certain extent, it partakes of the 

 natures both of the trunk and of the limbs. It is like the 

 limbs in that it is solid, that it contains no body-cavity, 

 and is not traversed by the alimentary canal. 



It is like the trunk in that it contains a prolongation of 

 the vertebral column, and of the neural canal. In the 

 head, we saw that the neural canal expanded, it receives 

 its anterior enlarged termination — the brain. In the tail 

 the neural canal contracts, and soon ceases, as it incloses 

 the progressively diminishing posterior end of the neural 

 axis— the termination backwards of the spinal marrow. 



Let us examine the bones which form the cat's tail a 

 little closely. They are about a score in number. The 

 first seven or eight are all in the form of rings of bone, 

 but behind these the vertebra; become merely more or less 

 elongated solid bony cylinders, which get gradually 

 smaller till they become mere rudiments of vertebrae. 

 Beneath the vertebrae run blood-vessels, and on all sides 

 are muscles which serve to bend the tail in all directions. 



Such is the structure of the tail in this animal, its use 

 (or "function ") is not very important. Cats can live very 

 well without their tails, and the well-known Isle of Man 

 variety — the Manx cat — has scarcely more visible tail 

 than we have ourselves. Yet the cat's tail no doubt aids 

 to a certain extent in maintaining the balance of the body in 

 the animal's various motions, and especially perhaps in 

 climbing. Everybody has noticed the lateral undulations 

 of the end of the tail of a cat which is watching a mouse, 

 and it is curious to note how the wagging of the tail in 

 the cat and the dog respectively, accompany very different 

 emotions. 



The gesture language of these two animals as expressed 

 by the motion of their tails, and, indeed, by various other 

 motions, is exceedingly different. 



The structural characters which have been noticed 

 concerning the cat's tail arc substantially similar in all 

 other beasts. In all, the tail is formed by a prolongation 

 of the back bone (with more or less of neural canal), but 

 has no body-cavity, and is not traversed by the alimentary 

 canal. 



But, although the essential structure in all beasts is 

 similar, there are certain subordinate differences which 

 merit our attention in the form of the tail in different 

 beasts. 



Dogs and cats belong to a great group of flesh-eating 

 beasts, called, from their predominant mode of feeding, 

 " carnivora." Bears, weasels, badgers, civet-cats, seals, 

 and sea-bears, also belong to this group. 



If you enter the small mammalia house you may see 

 a beast allied to the badger and weasel, called the 

 kinkajou. This animal is an inhabitant of Brazil, and 

 its tail bears a relation to the region it inhabits. 



The animal lives in trees which it roams over in search 

 of small animals on which it preys, such as birds' eggs and 

 bees' nests, and these nests its sharp strong claws can tear, 

 while it has an extremely long tongue, capable of being 

 thrust into the cells and extracting the honey. But its 

 tail, which is very long, is specially modified to assist it 

 in its mode of life. The end of the tail is curled round, 

 and is capable of strongly grasping any object about 

 which it may be twined. 



This kind of tail is called a " prehensile tail," and acts 

 as a fifth grasping organ, in addition to the two hands 

 and the two feet. 



It is in this prehensile character that the kinkajou's 



