VEKTEBRATE ANIMALS. 



callud the shoulder-blades, which lie upon the ribs, 

 and are kept in their proper position partly by the 

 action of powerful muscles, and partly by the support 

 aflbrdcd them by one or two pairs of bones which spring 

 from the front of the breast-bone; those bones are often 

 \yanting. The hinder extremities, on the contrary, 

 are usually articulated to a strong bony ring or basin 

 (the pelvis) which is firmly attached to the vertebral 

 column below the loins; the vertebrae of this part of the 

 spine being also completely united to each other, so as 

 to form a single bony" piece (the sacrum). 



In the essential structure of the limbs there is a 

 wonderful uniformity throughout the whole of this 

 great group of animals. Each limb consists of four 

 distinct parts, wliich correspond exactly in the anterior 

 and hinder extremities, although, in conformity with 

 the usages of human anatomists, they have received 

 diifereut names in the two pairs. In the fore-limb 

 the bones are the arm-bone, the two bones of the 

 fure-arm, the bones of the wrist, and those of the 

 hand; in the hind-limb they are the thigh-bone, the 

 two bones of the shank, the heel-bonoo, and those of 

 the foot. The arm-bone and thigh-bone {Jnimerus and 

 femur) articidate respectively with the shoulder-blade 

 and pelvis ; they are single bones, usuidly of a cylin- 

 drical form. The fore arm and the shank include two 

 parallel bones (called the ulna and racUm in the arm, 

 the tibia and Jihula in the leg), one of which, in each 

 aiend)er (the ulna and the tibia), is united by a hinge- 

 like joint with the lower extremity of the arm or 

 thigh-bone, forming the elbow or the knee. The 

 other bones (radius and Jibula) are scarcely, if at all, 

 attached at this joint ; they are consequently capable 

 of rotating to a certain extent, and thus enable the 

 hand or foot to be turned in various directions. It 

 is to the broad extremity of these latter bones that 

 those of the wrist and heel {carpal and tarsal hones) 

 are attached; these are numerous short bones, packed 

 closely together, but still capable of a greater or loss 

 freedom of motion. They are followed by the bones of 

 the hand and foot [metacarpal, metatarsal, and diijited 

 bones), which frequently form five rays of three or 

 four joints in each, starting from the wrist or heel. 

 Of those the metacarpal and the metatarsal bones 

 constitute the palm of the hand and the sole of the 

 foot in man; the digital bones, which are also called 

 phedanges, form the fingers and toes. 



It is not to be supposed, however, that all these 

 parts present themselves to our notice with equal 

 distinctness in every creature formed upon what is 

 called by naturalists the vertebrate type ; in fact, we 

 meet with an almost endless variety of modifications in 

 the different regions of the body, but especially in the 

 hmbs; and the study of these modifications, of the 

 wonderful series of changes, by which the Creator of 

 all tilings, submitting himself, as it were, to a self- 

 imposed law, has adapted the same general type of 

 Btructure to the most dissimilar purposes, is not only 

 one of the most interesting branches of zoology, but 

 also one of the most striking proofs fmnishcd by 

 natural theology of the prevalence of an intelligent 

 design in Animated Nature. 



It is the business of the philosophical anatomist to 

 investigate these marvellous modifications of structure; 

 to trace the plan by which the same organs have been 

 adapted to the most difl'erent offices, and to endeavour, 

 by deducing therefrom the abstract or ideal form from 

 which all the special structures presented to our obser- 

 vation may be derived by variations in the degree of 

 development of the different parts, to obtain a typo 

 with which things, apjiarently the most dissimilar, may 

 be compared : and thus to enter, as it were, into the 

 mind of the great Designer of the universe. It is, how- 

 ever, unnecessary here to dwell at any length upon this 

 most interesting branch of science, and we shall there- 

 fore content ourselves with giving a very brief abstract 

 of the general results which have been obtained by 

 much earnest thought on the part of some of the great- 

 est minds of the present century. 



According to the generally received views, the 

 skeleton of a vertebrate animal is composed of 

 numerous segments or vertebraj (the latter term being 

 used in an ideal sense). Even the skull itself is proved 

 to consist of several vertebrfe developed in a remark- 

 able manner — the bones of the face holding the same 

 relation to those of the true skull, that the ribs do to 

 the superior arch of the dorsal vertebrte through which 

 the spinal cord passes. The four limbs are appendages 

 of two particular vertebral segments; and similar appen- 

 dages are met with in a rudimentary form upon other 

 segments in some animals. 



Regarding the skeleton in accordance with these 

 views, as consisting ideally of a series of similar seg- 

 ments, we find that it is by the suppression of certain 

 parts of some of these, and the greater or less develop- 

 ment of others, that the varied forms of vertebrate 

 animals are produced. The appendages constituting 

 the limbs are, as already stated, usually suppressed 

 completely in all but two segments, and the ribs often 

 share the same fate in the neck, loins, and tail. In 

 other cases the bones of one or both pairs of limbs are 

 wanting, and in some of the lowest forms we find nothing 

 left but the vertebral column itself, which sometimes 

 is not even ossified, but consists of a gelatinous or car- 

 tilaginous cord, running, with little or no trace of any 

 division into vertebra;, from the head to the extremity 

 of the tail. 



Yet throughout all these variations the intelligent 

 observer traces one uniform plan : the great centre of 

 the nervous system always consists of a brain and 

 spinal cord, supported in all but one instance, by a 

 structure which may be recognized as a vertebral 

 column; the jaws are always supported by bones or 

 cartilage beneath the skull, and tlieir opening is always 

 horizontal ; the limbs are never more tlian four in 

 number ; the heart is always muscular, and connected 

 with a distinct system of vessels, through which courses 

 a blood, coloured red by innumerable globules ; and 

 the organs of the four special senses (sight, lioaring, 

 smell, and taste) are almost always highly developed, 

 and invariably placed in cavities of the face and head. 

 The viscera are veiy similar in their nature throughout 

 the entire group, and the animals are always male or 

 female, never hermaphrodite. 



