ANIMALIA VERTEBRATA— VERTEBRATED ANIMALS. 



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for a lonn; time unconsolidated, and there appears between them a quantity of matter 

 purely gelatinous, capable of being dissolved by boiling water. The extremities, while 

 separated, are called epiphyses, while that in the body of the bone is termed diaphysis. 

 In the flat bones, the centres of ossification may be compared to suns, of which the bony 

 fibres are the rays, rendered visible through the semi-transparent cartilage by their 

 opaque whiteness. These centres vary their appearances in different bones : in the 

 round bones they resemble small grains or nuclei, but in the angular bones they assume 

 a great variety of forms and positions. 



When the fibres of one centre have advanced so far as to come every vrhere in con- 

 tact with those next to them, the bones are then only separated by sutures, which 

 may afterwards be more or less promptly effaced. Some of these fibres turn aside to 

 the right and left, and thus produce the appearance of lattice-worli ; while new strata, 

 placed above and below the former, cause the texture of the bone to assume a lamel- 

 lated aspect, 



"We are in the habit of considering as single bones, all those of which the different 

 parts ossify and unite in youth, as the vertebree, the occipital and frontal bones ; 

 while we. consider those that do not form a union with the neighbouring bones until 

 an advanced period of life, as distinct. Thus the frontal bone, which sometimes 

 remains separate from the parietal bones to a very old age, is regarded as a distinct 

 bone ; while at the same time it is composed of two parts, which frequently remain 

 separate xmtil the age of thirty or forty. 



Ossification is not found to proceed with an equal rapidity, whether we consider k 

 in each kind of animal, or in the different bones of the same animal. In Man, and all 

 other Mammalia, we observe that the bones of the internal ear are not only first 

 ossified, but that they surpass all others in density, and in the quantity of calcareous 

 phosphate they contain. Thus, the bone of the cavity of the tympanum in the 

 Cetacea, but particularly in the Whale and the Cachalot, is superior to marble in 

 hardness and density. Its section appears equally homogeneous, and exhibits no vestige 

 of fibres, lattice- work, or vessels. On the contrary, other bones are very slow in 

 acquiring the consistency they ultimately possess. The epiphyses, for example, do not 

 oflsify until long after the bodies of the bones to which they belong. Finally, there 

 are some cartilages, which, in certain classes of animals, never admit a quantity of 

 calcareous phosphate sufficient to render them completely bony; such as the cartilages 

 of the ribs, and the larynx. It is certain, therefore, that there are several cartilages 

 which are never converted into bones, although there is no bone which did not for- 

 merly exist in ihe state of cartilage; yet, there is a general tendency in all gelatinous 

 parts to receive calcareous matter, as the tendons, and several white parts, ossify with 

 greater facility than the others. The same difTcrences which exist in this respect 

 between the several bones of the same species, are also found to exist between species 

 and species, on comparing the entire skeleton. 



We not only find that the bones of an animal are slow in arriving at the degree of 

 hardness which belongs to them, in proportion to the period of the growth of the 

 animal ; but we further know, that there arc some animals in which ossification is 

 never complete, and whose skeletons are always cartilaginous. This is the case with 

 Sharks, Rays, Sturgeons, and all those Fishes which arc thence called cartilaginous, 

 or Chondropterygii. Although the bones of the other Fishes, and of many Reptiles, 

 attain a greater degree of hardness, they still, however, preserve much more flexibility, 

 and retain a far greater proportion of the gelatinous substance, than the bones of 

 animals having warm blood. They grow, therefore, during the whole period of their 

 existence ; because it is cartilage only that can grow. On the contrai-y, when once 

 the bones have attained their proper degree of hardness, their dimensions cannot alter ; 

 and the animal can only increase in thickness. At this period, the animal economy 

 commences a retrograde movement, and the first steps are made towards old age and 

 decrepitude. 



Animals differ greatly in respect to the texture of the bones, and the cavities of 

 Tarious kinds formed within them, as well as in the rapidity of ossification, and in the 

 proportions which the constituent parts of bone bear to each other. In Man, the in- 

 ternal texture of the bones is very fine. The laminae of their spongj- substance are 

 amall and close ; and where this texture is most unlike lattice-work, it exhibits long 

 and dehcate fibres. In Quadrupeds, the texture of the bones is in general coarser; 

 in the Cetacea, it is more loose, the cells are larger, and the lamina; which form them 

 much broader. It is easy to distinguish their external fibres, which in the jaws and 

 ribs of Whales and Cachalots may be rendered as evident, by long maceration in 

 water, as the fibres of half-decayed wood. With respect to size, however, they seem 

 to bear no relation to the magnitude of the animal to %vhich they belong. The bones 

 of Birds are of a slender, firm, and elastic nature, and seem formed of lamina; soldered, 

 the one over the other. The bones of Reptiles and Fishes are in general more homo- 

 geneous, and the cdcareous particles seem more uniformly distributed throughout the 

 gelatinous substance. This observation appears the more striking as we approach the 

 cartilaginous Fishes, in which the gelatinous substance completely overcomes, and ap- 

 pears to conceal, the phosphate of Ume. 



Several animals have no large medullary cavities even in their long bones. There 

 are none in the Cetacea and Seals. Caldcsi and Cuvier have long remarked the same 

 thmg m respect to the Tortoise. The Crocodile, however, has these cavities very distinct. 



In some bones we find other cavities, called s^iimses, which contain no marrow. 

 Thsy all communicate, more or less directly, %vith the exterior of the body. Man has 

 sinuses in the frontal, sphenoid, and maxillary bones of the skull. In several Mam- 

 malia, these sinuses extend much farther backwards, and penetrate throuf^h a Treat 

 part of the body of the cranium. In the Hog they proceed as far as the occiput; 

 and it is these which swell so singularly the cranium of the Elephant, and which 

 superficial observers are apt to mistake for an extraordinary devolopiucnt of the brain. 

 In Oxen, Goats, and Sheep, these sinuses extend even into the centres of the horns. 

 The Gazelles are the only animals with hollow horns, having the nucleus of their 

 horns sohd or spongy without any large cavity. 



Other smuses exist m the temporal bones ; these communicate with the cavity of 

 the tympanum. These are particularly extensive in Birds, and occupy as much space 

 as the nasal sinuses do m Quadrupeds. They produce the same effect on the cranium 

 gf the Owl, as the other kinds of sinus produce on that of the Elephant. 



The growth of the horns of the Deer present singular phenomena, which will ba 

 described in their proper place. 



The blood of the Vertehrata is always red; and it appears to possess 

 a peculiar composition, fitted to preserve that energy of sensation and 

 muscular vigour observable in this division of animals. These properties, 

 however, greatly depend upon the degree of perfection in which respira- 

 tion is performed; and this circumstance gives lise to the subdivision 

 of the Vertebrata into four classes [Mammaha, Birds, Reptiles, and 

 Fishes.] 



The external senses are always five In number ; and they reside in two 

 eyes, two ears, two nostrils, the integuments of the tongue, and those of 

 the whole body. Certain species seem [at first sight] destitute of eyes. 



But this is only apparent, as all the Vertebrata have two eyes composed of the 

 same essential parts as those of Man. The only apparent exceptions are the Miis 

 typhlus, or Blind Rat, where the eyes are concealed under the skin; and the Fish 

 called Cohitis anahUps^ where the same eye, having two pupils, appears double. 



The nerves reach the marrow through the holes of the vertebrce and 

 of the skull; and they all appear to become incorporated with it. After 

 interlacing its filaments, the marrow expands itself in forming the various 

 lobes of which the brain is composed, and terminates in two arched 

 masses called hemispheres; the volume of which is [sometimes] propor- 

 tioned to the degree of intelhgence possessed by the animal. 



Most of the nerves of the trunk and of the limbs arise from the spinal marrow, 

 whence they are distributed, and through their means sensation and motion are trans- 

 mitted to the several parts of the body. "W^ien any portion of the spinal marrow is 

 compressed or divided, all those parts to which nerves are transmitted, arising from 

 the portion of the spinal column situate below the part compressed, are immediately 

 paralyzed and deprived of sensation and motion. In some species remarkably tena- 

 cious of life, a remnant of consciousness will remain, even after the entire separation 

 of the brain and spinal cord. If the head of a serpent be removed, and shortly after- 

 wards the skin of its tail be punctured by a sharp instrument, the headless trunk will 

 turn instinctively to defend the part attacked. 



The internal structure of the spinal cord is well exhibited on makinn- a section of 

 th? spine of a Carp. Its spinal cord is composed of six columns running parallel, 

 and arranged symmetrically round a central canal filled generally with fluid. The pair 

 of columns situate behind are appropriated for sensation, and the two in front for 

 voluntary motion. Fibres are transmitted from each side ; these unite and form nerves, 

 yet the fibres still retain their characteristic functions. The nerves of sensation have 

 small ganglions or knots near the central column ; and the whole are formed into one 

 system by the sjTnpathetic nerve, which is parallel to the spine, and passes near it on 

 each side. 



There are four principal portions of the Human Brain — J, the Medulla oblongata; 

 2, the Cerebellum; 3, the Cerebrum; and 4, the Optic tubercles. Besides these, there 

 are many intricate parts, which we shall not attempt to describe in this outline. 



1. The IMedulla Oblongata is that part of the brain which forms the immediate 

 continuation of the spinal cord. It appears to contain the portion most essential to 

 life and consciousness. Every other part of the brain may be successively taken awav, 

 at every mutilation the sphere of vital action may be diminished ; yet, if the Medulla 

 ohlongata be preserved entire, nay, even if that minute portion near the origin of 

 the fifth and eighth nerves be iminjured, the animal will still exhibit marks of instinct 

 and sensation. Upon removing the cerebrum, cerebellum, and tubercles of a living 

 hedge-hog, M. Magendie found that the anim.al was rendered blind; yet it rcmamed 

 acutely sensible to smell, taste, or bodily punctures; and its powers of locomotion were 

 unimpaired. Infants are sometimes born acephalous, that is, without a brain, anA 

 possessed only of the Medulla oblongata, nerves, and spinal cord. Wlien they sur- 

 vive for a short time after birth, which docs not often happen, they always possess 

 sensation and motion. Yet their brain only resembles that of the MoUusca, such as 

 the snail or the oyster. One infant, described by Mr Lawrence, survived four 

 days. " The brain and cranium of this infant were deficient, and the basis of the 

 latter was covered by the common integuments, except over the foramen magiiuTvi 

 (or that hole in the skull which communicates with the vertebral column), where 

 there existed a soft tumour, about equal in size to the end of the thumb. Tiio 

 smooth membrane covering this was connected at its circumference to the skin. The 

 child, as is generally the case in such instances, was perfectly formed in all its other 

 parts, and had attained its full size. It moved briskly at first, but remained quiet 

 afterwards, except when the tumour was pressed, which occasioned general convul- 

 sions. It breathed naturally, and was not observed to be deficient in warmth, until 

 its powers declined. From a fear of alarming the mother, no attempt was made ta 

 see whether it would take the breast; but a little food was given it by the hand." 

 From these instances, it appears that the brain is not essentially necessary to the 

 perfcrmance of the ordinary instinctive functions of an animal ; but that it is the 

 Medulla oblongata which forms the essential organ. If the head of a tortoise or frog 

 be cut off, sensation will remain either in the separated head, or in the headless trunk, 

 according as the section has been made above or below this vital part. It is a curious 

 fact, that the usual effects of an emetic are prevented by pressure on the Medulla 

 ohlongata, or vomiting is instantly arrested, if it has already commenced. 



2, The Cerebellum, or little brain, is the tubercle or tubercles arising from the 

 expansion of the hinder portions of the spinal marrow. It would therefore appear to 

 be more especially designed for sensation. In Man, the Cerebellum is composed of 

 two large hemispheres, connected together by the vermiform processes, so as to form 

 one structure, being composed of a white nervous substance, enveloped in a uniform 

 covering of gray matter. When this part of the brain is injured, the animal is affected 

 with a kind of giddiness, by which it appears to be hurried forwards. In attempting 



