157 



AMPHIBIA. 



AMPHIBIA. 



158 



of them is very wide ; so wide, indeed, in some (the large Frogs and 

 Pipas, for instance), as to admit of their swallowing vertebrated 

 animals; but insects, anuelides, and small mollusks form the chief 

 of their food. They have no true fleshy lips, nor indeed have any of 

 the Reptiles ; but the fresh-water tortoises are furnished with folds of 

 skin as a covering for their cutting jaws, and perhaps as a more 

 complete apparatus for shutting the mouth. The same conforma- 

 tion is observable in the greater number of the Tadpoles of the 

 Batrachians, the larger portion of which, in their adult state, have 

 the lower jaw received under a soft skin which covers and edges the 

 mandible. The branches of the lower maxillary bone are rarely 

 soldered at the symphysis, and sometimes, as in the genera Rana 

 and Hyla, there is, at the point of junction, a mere cartilage which 

 admits of a certain amount of motion. In the Frogs and the Urod&les, 

 the number of pieces composing each of the branches amounts to three. 

 One of these pieces corresponds with the symphysis, and is armed with 

 teeth ; the second serves for articulation, and the third is situated 

 backwards, and prolonged below. On the palate of many of these 

 Amphibia are certain processes which may be termed teeth ; but these 

 are pointed, and not tubercular, as the old error of naming some of the 

 teeth of fossil fishes Bufonites might lead us to suppose. These palatal 

 teeth form a part of the bones to which they are attached, as in the 

 case of fishes. 



The tongue performs a leading part in the capture and deglutition of 

 the prey. In the greater portion of this group the structure of this organ 

 is altogether anomalous, and its insertion is equally at variance with the 

 mode adopted hi the other vertebrated animals. It is very soft, fleshy 

 almost throughout, and is not supported at its base by an os hyoides. 

 Its attachment is the reverse of that generally seen, for it is fixed in 

 the concavity which is formed by the approach of the two branches of 

 the lower jaw towards the symphysis. In a state of repose, and when 

 the mouth is shut, this tongue, which has its root, so to speak, in the 

 interior edge of the anterior part of the lower jaw, has its free extremity 

 in the back part ofthemouthand before the aperture of the air-passages ; 

 but when the animal puts it forth, it is considerably elongated and 

 thn >wn sharply out of the mouth, as if by an effort of expulsion. The 

 end reaches to a considerable distance, as, turning on the pivot of its 

 anterior fixture, it is reversed in such a manner that the surface which 

 was below when the tongue was in the mouth, and in a state of repose, 

 ia, when it is thrown out, above ; and when the tongue is returned 

 into the mouth, the surface, which was an instant before above, 

 resumes its original position, and is again beneath. The organ is 

 armed with a tenacious viscous secretion ; and when it touches the 

 prey, the latter adheres so firmly to it, that it is carried back with the 

 tongue into the mouth. There it is, in most cases, compressed, involved 

 again in a glutinous sort of saliva, and almost instantly submitted to 

 the act of deglutition. The motion of throwing out and returning 

 the tongue is often performed with a rapidity which the eye can 

 hardly follow. If any one will observe a toad in a melon-frame, he 

 will see the ants or other insects which come within shot of its tongue 

 disappear ; but his vision must be very acute and prompt to detect the 

 action of the tongue. The muscles, whose office it is to move the bones, 

 cartilages, and other parts of the mouth, act more especially upon the 

 lower jaw, upon the bone of the mandible, and upon the tongue, which, 

 after being shot forth as we have endeavoured to describe, is returned 

 and swallowed, as it were, with the captured prey, and the act of 

 deglutition is continued till the food is lodged in the stomach. 



The pharynx in mammiferous animals consists of that backward 

 cavity of the throat, into which the lower orifices of the nostrils, the 

 orifice of the mouth, the canal of the ear, the larynx, and the oesophagus 

 open ; but in the reptiles there cannot be said to be any true pharynx ; 

 for the nostrils, as well as the glottis, open into the mouth, the oeso- 

 phagus commences immediately behind the nostrils, and the muscles 

 that act> more especially upon these parts and upon the tongue are 

 those that begin the act of deglutition : we shall presently see that 

 these same muscles are also put in requisition to force the air necessary 

 for respiration into the glottis and trachea, in order to supply the 

 cavity of the lungs. The stomach of the Anourous Amphibia does not 

 require any particular notice ; but the maxim that the more carni- 

 vorous an animal is, the shorter and the less flexuous is its intestinal 

 canal, is well illustrated in that tribe. The Tadpole, which lives upon 

 vegetables, possesses an extremely long digestive tube ; but in its 

 perfect state, and when its appetite has become altogether carnivorous, 

 the intestines become very much shortened, losing four-fifths of the 

 length which distinguished them when the animal was in its early stage 

 of existence. The vent is rounded and wrinkled. The liver generally 

 consists of three lobes, and the gall-bladder adheres to and is hidden 

 in the concavity of the liver, very high up. The spleen in the Frog 

 and Toad is rounded, not of large dimensions, and situated in the 

 mesial region, under the intermediate lobe of the liver. There is also 

 a pancreas, and the chyliferous veins may be distinctly traced. The 

 digestive organs vary considerably in the Tadpole. In this early stage 

 they have a mouth furnished with lips, and horny cutting processes, 

 that act as jaws in the division of the vegetable food which forms their 

 prim ipal nourishment, and their intestinal canal is coiled spirally 

 within their Urge rounded abdomen. The metamorphosis is complete, 

 internally a well as externally, when this armed little mouth is 

 changed into the widely-opening gape, which reaches beyond the eyes, 



and the animal swallows its living prey entire. In this their last stage 

 they can endure a long abstinence. They grow slowly, and they live 

 to a considerable age. The skin which edges their jaws is soft, 

 and forms a sort of gum or external lip ; their under-jaw is received 

 into a kind of rim or groove, which runs along the upper-jaw, and its 

 two branches are slightly moveable towards the symphysis : this 

 junction of the jaws is as complete as the shutting of a well-fitted 

 lid of a snuff-box. 



Circulating System. The circulation in the Anourous Amphibia varies 

 with the different metamorphoses which the animal undergoes. In 

 the early or tadpole stage the whole of the blood is driven by the heart 

 into the branchial vessels, the circulation at that period being the same 

 as it is in fishes. The apparently single auricle (for according to the 

 observations of Dr. Davy and of Messrs. Saint Ange and Wdbert, it is 

 in fact separated into two divisions), or rather the partition which 

 exists at the point where the oxygenated blood arrives through the 

 pulmonary veins, can hardly be said to be distinct, and the venous 

 blood, which is poured into it by the large vena cava, penetrates 

 finally into the single ventricle, which, by contracting, pushes the blood 

 into the single arterial trunk, furnished at its base, near the valvules, 

 with a sort of bulb, or contractile swelling. This artery, which 

 contains the black or venous blood, is divided into two trunks, one 

 directed to the right, the other to the left ; and these are then sub- 

 divided into two, three, or four branches, according to the number of 

 the branchial leaflets : on their arrival there, they inosculate with the 

 venous trunks, and by that time the blood has assumed its arterial 

 quality and colour. These arterial veins unite successively, so as to 

 form, by means of two principal trunks, the origin of one great artery, 

 or aorta descendens, which is, at the point of its formation, placed 

 near the head, to which it gives off many branches, and continues to 

 descend down the vertebral column. 



But when the time of metamorphosis arrives, and when the animal 

 which had been breathing by means of gills is to respire through the 

 medium of lungs, an entire and necessary change takes place. In 

 proportion as the branchiae of the Tadpole are destroyed and absorbed, 

 the calibre of the venous arteries, which were distributed to them, 

 diminishes gradually, till they are at last entirely obliterated. The 

 first of these vessels then develops itself, and receives on each side the 

 whole of the blood, giving off three principal trunks one for the 

 head, corresponding to the carotid artery ; one for the anterior limbs, 

 or a branchial artery ; and one, the longest of all, for the cellular lung, 

 which is of considerable volume. The rest of the principal trunk 

 follows the mesial line, and unites with its congener, so as to form a 

 true aorta for the supply of the viscera and lower extremities, which 

 acquire their large dimensions at this period. 



Respiratory System and Vocal Organs. The absence of the ribs prevents 

 any application of costal influence upon the respiratory organs of the 

 Anourous Amphibia, as is the case with the mammiferous animals; but 

 though their form; as well as the medium in which they live, is so 

 totally different in the early and late part of their life, the principle of 

 action on these organs is nearly the same. The young may be said 

 to swallow water, or at least receive it into the cavity of the mouth, 

 before they force it into the branchial vessels ; and though the mode 

 of breathing is so entirely changed in after-life, the operation consists 

 in the perfect animal of a succession of deglutitions of air. 



When the Amphibia leave the egg, their branchiae appear externally 

 like little coloured fringes on each side of the neck, and so they remain 

 in the Urodiles, as long as their lungs are not sufficiently developed to 

 serve for complete respiration. But in the Frogs and the Anourous 

 A mphibia the first stage of the animal's life endures but a short time. 

 It soon assumes the Tadpole form, with an enormous belly and head, 

 in one undistinguished outline, and a long tail. At this period the 

 branchiae, or gills, are hidden, being contained in a cavity, and then 

 the water enters the mouth by the orifice of the nostrils, which are 

 supplied with valves. When in the cavity of the mouth, which is 

 well closed on all sides, with the exception of the throat, where are 

 placed the branchial slits, the water, acted upon by the muscles which 

 cover them, traverses these spaces, and bathes the branchire before its 

 exit through the branchial holes. The blood which is pushed into 

 these branchiae is then distributed, as it is in the fishes, and passes, as 

 we have seen, from the arterial venous vessels into the arteries which 

 unite to form the aorta. 



On acquiring their perfect form, and when the obliteration of 

 certain points, and the development of the others, have adapted the 

 Anourous Amphibia for breathing air, by means of its two large 

 lungs, the muscles employed in deglutition are the great agents for 

 carrying on the respiration. The anterior nostrils, as we have before 

 stated, open nearly straight, by means of simple apertures in front of 

 the palate ; the tongue is applied as a kind of stopper upon the back 

 nostrils, and the trachea is terminated by a glottis opening into the 

 mouth. The air thus imprisoned is forced or pumped at each gulp 

 through the glottis, to be distributed over the lungs. 



In the museum of the Royal College of Surgeons are several 

 preparations, illustrative of the aeration of the blood, by means of 

 branchiae, in the early stage of Rana paradoxa, and also of the mode 

 of respiration in the adult forms of the same group of animals. 



The activity of respiration is increased in proportion to the elevation 

 of the temperature of the surrounding air. M. Delaroche found that 



