96 



AMPHIBIA. 



bony plates on each side, probably rudiments 

 of the vomer and palatine bones. Each of 

 the larger has six or seven lines of teeth, about 

 twelve on each line; and each smaller bone 

 bears four ranges of five or six teeth ; making 

 in all nearly two hundred teeth in the palate. 

 Those of the lower jaw in this animal are 

 placed in similar order. In the proteus the 

 teeth nearly resemble those of the salamander. 



The maxillary teeth are always slender, 

 sharp-pointed, and closely -set. The frog has 

 about forty on each side of the upper jaw, of 

 which eight belong to the intermaxillary bone. 

 The salamander has about sixtyabove and below. 



In the tadpole state of the frog the mouth 

 is very small, and, instead of teeth, is occu- 

 pied only by minute horny plates of just 

 sufficient consistence to abrade the soft mixed 

 food which it finds on the surface of animal 

 or vegetable substances in the water. Its sto- 

 mach and intestinal canal are of very different 

 form from that which they afterwards assume. 

 The intestine is of nearly equal size throughout 

 its whole length. It is very long, being not 

 less than ten times the length of the actual 

 space from the mouth to the anus, and is coiled 

 up in a circular form, occupying the greater 

 part of the abdominal cavity. The canal, as 

 we shall presently see, changes its character 

 materially during the metamorphosis of the 

 animal, becoming gradually shorter until it is 

 not a quarter of the length, in proportion to 

 the size of the animal, which it exhibited in 

 its earlier condition. 



In the adult amphibia the whole alimentary 

 canal is of a very simple character. The 

 oesophagus is wide and comparatively short. 

 The stomach single, consisting of a simple sac, 

 elongated in the lengthened forms of the sala- 

 mander, the proteus, and other aquatic species. 

 The intestine is but slightly convoluted, even 

 in the short tailless family ; and there is com- 

 paratively little difference in the diameter of 

 its two distinct portions. It terminates, as in 

 the reptilia, in a cloaca, or pouch, which also 

 receives the openings of the urinary and genital 

 organs. The anus in the toads and frogs opens 

 on the hinder part of the back ; in the other 

 forms it is situated beneath at the commence- 

 ment of the tail, as in the reptilia. 



The liver, the pancreas, and the spleen are 

 found in the whole of the amphibia ; and 

 these organs are observed, in the elongated 

 aquatic forms, to assume a corresponding 

 lengthened shape. The liver is of considerable 

 size, particularly in the salamanders. The 

 gall-bladder exists in all cases, varying, how- 

 ever, in size and form in the different genera. 



IV. Lymphatic and lacteal system. This 

 system is highly interesting in the amphibia, 

 on account of its extreme development, and 

 of its presenting several important and remark- 

 able peculiarities in its structure. 



The investigations of Professor Muller of 

 Berlin have lately brought to light the existence 

 of pulsating cavities in the course of the lympha- 

 tics, constituting a sort of ventricles for the pro- 

 pulsion of their fluids towards the veins into 

 which they are received. In the frog two pairs of 



these little pulsating sacs are found ; at the pos- 

 terior part one is situated on each side of the 

 extremity of the coccygeal bone, behind the hip- 

 joint, and the anterior ones under the posterior 

 edge of the scapula by the transverse process 

 of the third vertebra. These cavities are of 

 considerable size, and pulsate with some degree 

 of regularity : the pulsations, however, do not 

 coincide with those of the heart, nor are those 

 on the one side always synchronous with 

 those on the other. The posterior ones convey 

 the lymph received from the legs and hinder 

 parts of the body into the ischiatic veins, and 

 the anterior pair, into which the absorbents 

 of the arms and the anterior parts of the 

 viscera, &c. open, convey this fluid into the 

 jugular veins. The internal structure of these 

 sacs is cellular; they communicate freely 

 with each other on each side by anastomosing 

 vessels. On inflating the organ, not only the 

 lymphatic vessels are inflated, but the whole 

 of the veins also. Dr. Marshall Hall had 

 previously observed a somewhat similar pul- 

 sating cavity in the eel. 



These lymphatic ventricles in the amphibia 

 have still more recently received further exami- 

 nation and illustration by Professor Panizza 

 of Pavia, who published the result of his 

 researches in the year 1833.* Professor Muller's 

 discovery was published in the previous year 

 in the Berlin Annals. 



The lymphatic system is developed to an 

 extraordinary degree in the frogs, as well as 

 in several other genera of this class, its vessels 

 being found in numbers and of considerable 

 size immediately under the skin. 



The lacteals ramify upon the surface of the 

 intestine in two layers, anastomosing and 

 forming intricate plexuses on the mesentery, 

 and terminating in two trunks, or thoracic 

 ducts, which pass forwards one on each side 

 of the spinal column. 



V. Of the sanguiferous system. If the 

 changes, so frequently alluded to, which the 

 animals of this class undergo in passing from 

 the condition of a fish to that of a reptile, have 

 received repeated illustrations in the considera- 

 tion of the structure of the skeleton, of the 

 organs of motion, and of those of digestion, far 

 more interesting and important are those which 

 occur in the character of the circulation ; in 

 which the view which has been taken of the 

 true situation of the amphibia in the chain of 

 animal development receives the most satis- 

 factory proof. Beginning life with all the 

 essential characters of the fishes, even in the 

 functions of circulation and respiration, pos- 

 sessing the single branchial heart of that class, 

 how wonderful and beautiful are the changes 

 which these systems of organs undergo, as the 

 branchiae become obliterated to give place to 

 pulmonic cavities, and the heart at the same 

 time assumes the compound character and form 

 of a systemic and pulmonic heart, in accordance 

 with the change in the respiratory organs. 



The newts, or water-salamanders, afford the 

 most satisfactory opportunity of observing these 



* Sopra il sistema linfatico dei rettili. fol. Pav. 

 1833. 



