Besides these general works, in which the anatomy of all or of most classes of animals is considered, there are several publications of distinguished merit, that contain a view of the structure of particular classes, tribes, or spe cies. Thus, the structure of the MAMM ALIA has been explained by D'Aubenton in Buffon's Natural History of Quadrupeds ; by Vic d'Azyr, in the Anatomic Comparee of the .Encyclopedie Methodigue ; by Stubbs, in his ?ina tomy of the Horse ; by Vitet, in his Medicine Vetcrinaire ; by Cuvier in the Annales de Museum .Kational Histoire Nature& ; and by Tyson and Home, in the Philosophical Transactions. That of the CETA CEA has been described by Mr John Hunter, in the Philosophical Transactions ; that of BIRDS, by Vicq d'Azyr, in the Memoires de l'AcademieWes Sciences, for 1772, and by Mr Maeartney, in the article BIRDS, of Rees's Cyclopedia ; that of REPTILES and SERPENTS, by La Cepede in his Histoire Xaturelle des Quadrupedes Ovipaires et Serpents, and by Townson, in his Tracts and Observations on Natural His tory and Physiology ; that of FisnEs, by Rondelet in his work De Piscibus, by the second Monro, in his Physiolo gy of Fishes, and La Cepede in his Histoire JVaturelle des Poissons ; that of CRUSTACE A and 1NsEcTs, by Swam merdam, in his Biblia Naturx, and Latreille, in his His toire Xaturelle des Crustaces ; that of MOLLUSC A, by Lamarck, in his work Sur les Animaux Inyertebres, and Cuvier, in the Annales de Museum National ; that of Wonms, by Lamarck, as above quoted, and by Hooper in the Memoires of the London Medical Society, vol. v. ; and that of ZOOPHYTES, chiefly by Trembley, in his work Sur les Polypes d'Eau Douce, and Baker in his Essays on the Microscope.
In the comparative view which we are here to take of the several organs in the inferior animals, we shall fol low the same arrangement which we have adopted in the preceding part ; but as the nature of our plan does not admit of our giving a very full account of these or gans, we shall confine ourselves chiefly to the differences and relations that take place in the several classes and orders under which animals have been arranged, accord ing to the most approved systems of zoology ; and we shall seldom extend the comparison to the genera of any particular order. Much less shall we examine thc dif ferences that subsist between the several species of a tribe, or the varieties of a species ; nor shall we attempt to point out, as in the human anatomy, the morbid ap pearances that have been discovered oh dissecting the inferior animals.
Before entering on the comparison of the organs in the order of the functions which they perform, it will be necessary to give a general account of the differences of structure according to which animals have been ar ranged under those groups which we call classes and orders.
On comparing animals in the most general point of view, we find that many have an internal articulated skeleton, the principal basis of which is a vertebral co lumn ; and that many others have either no articulated skeleton, or one that is external, and has no vertebral column. Hence animals have been divided into verte
bral and invertebral animals. Again, we find, on com paring together the vertebral animals, that some of them possess a heart with two ventricles, and that their san guiferous system contains warm blood ; while others have a heart with only one ventricle, and a sanguiferous system containing cold blood, or blood whose natural temperature scarcely exceeds that of the medium in which they live. Thus, we have two divisions of the vertebral animals, and these we may again subdivide ; the former according to their mode of generation, the latter according to their mode of respiration. Thus, of the vertebral animals, with a double heart and warm blood, some are viviparous, and suckle their young by mamma or teats. These animals arc called MaiammAA.
Others are oviparous, and do not suckle their young. These are the BIRDS. Of the vertebral animals with a single heart and cold blood, some possess lungs, as REr TILES and SERPENTS ; others breathe by means of gills, as FISHES.
On comparing the invertebral animals, we find that some of them have an external articulated skeleton or case, while others have neither skeleton nor articulated members. These two divisions of the invertebral ani mals may be subdivided according to the greater or less complexity of their organization. Thus, of the invertc bral animals with an external articulated skeleton, some have a circulating system, and breathe by branchix, and their skeleton is generally calcareous. These are called the CRUSTACEA. Others have no circulating system, but breathe by trache.c, and their external covering is horny. These are the INSECTS. Again, of the invertc bral animals without skeleton or articulated members, some have simple nerves, i. e. nerves without knotty protuberances, as those animals which we call MOL LUSC A ; others have knotted nerves, as \Valois ; while several have no appearance of nerves, and arc called Zoo ru YTES.
The MAMMALIA agree in having four articulated members, two atlantal and two sacral, though the latter, in many cases, and both in one order, are concealed be low the integuments, so as to resemble fins. They have two articulating condyles in the occipital bone ; their brain completely occupies the cavity of the skull, and is very complicated. Their internal car has at least three articulating bones, and a spiral cochlea ; only their lower jaw is capable of motion ; their larynx is furnished with an epiglottis; a muscular diaphragm is placed between the chest and belly, and there is an omentum covering the intestines on the sternal part of the belly. Their chyle is white, and passes through mesenteric glands, and their skin is more or less covered with hair. The male has 'a lienis, and the female an uterus, which has generally two horns.