432 



SUPPLEMENTAL NOTE ON REPTILES. 



and their sensations obtuse, with a slow digestion ; and 

 in temperate countries they pass the winter in an almost 

 constant state of torpidity. 



The brain in reptiles is proportionably small, and not 

 so essential to the exercise of their animal and vital 

 functions as to the mammalia and birds ; and their sen- 

 sations appear to be referred to a common centre, for 

 they continue to live, and exhibit voluntary motions long 

 after being deprived of their brain, and in many instances 

 after the head has been cut off. The connection of the 

 nervous system with the muscular fibre is also less 

 necessary to its contractions, and their muscles preserve 

 their irritability after being severed from the body much 

 longer than in the higher animals. The pulsations of 

 the heart have been knon - n to continue for many hours 

 after being separated from the body; and even without 

 it, the body will move for a considerable length of time. 

 It has been observed that the cerebellum in several of 

 the species is extremely small, which facts agree with 

 their slight propensity to motion. 



The smallness of the pulmonary vessels in reptiles en- 

 ables them to suspend respiration without retarding the 

 circulation of the blood ; this enables them to dive with 

 more facility, and to remain longer under water than 

 quadrupeds or birds. The cells of their lungs are also less 

 numerous, and generally large, in consequence of their 

 having fewer vessels to lodge on their parietes, and the 

 lungs take sometimes the form of simple sacs, scarcely 

 cellular in their structure. 



The whole class are provided with a trachea and 

 larynx, yet many of them are incapable of producing 

 articulate sounds. 



As their blood is cold, teguments for retaining heat 

 are unnecessary, and instead of these, therefore, they are 

 clothed with scales, or simply with a naked skin. 



The females are provided with a double ovary and two 

 oviducts, and the males of several genera are furnished 

 with furcated organs of generation, but the batrachians 

 are destitute of this organ. Those females which couple 

 deposit eggs which are protected by a shelly covering, 

 and those species which do not, produce soft and glary 

 eggs, destitute of any crust. These they abandon after 

 the deposition in some convenient situation ; but there 

 are a few species which carry them about with them. 

 The young is hatched perfect in its form in many species: 

 but there are other species, which, on quitting the ova, 

 have the organization of fishes, and whose form is not 

 perfectly developed until after a certain time has elapsed, 

 when they undergo a complete metamorphosis. This is 

 well exemplified in the frog being hatched as a tadpole. 

 These are provided with branchiae, or gills, like fishes, 

 and some of the genera retain these organs even after the 

 developement of their lungs. In several of the oviparous 

 reptiles, particularly in the coluber, the young animal in 

 the egg is formed and considerably advanced at the mo- 

 ment it is deposited by the mother ; and there are even 

 some species which may be artificially rendered vivipar- 

 ous, by simply retarding the time of laying the egg, 

 which M. Geoffrey St Hilaire has proved by depriving 

 the colubra of water. 



The quantity of respiration in reptiles is not fixed, as 

 is the case with mammalia and birds, but varies with the 

 proportions of the diameter of the pulmonary artery, com- 

 pared to that of the aorta. Tortoises and lizards, for 

 example, respire much more than frogs, &c. ; and hence 

 results a much greater difference of sensibility and ner- 

 vous energy than can exist between one mammiferous 

 animal and another, or between birds. 



A greater variety of form prevails amongst reptiles 

 than is found among the mammalia and birds, and it is 

 in the production of these forms that Nature seems to 

 have imagined shapes of the most fantastic description, 

 and modifying in every possible manner the general plan 

 which she has prescribed to herself in the vertebrata, 

 and iu the oviparous class in particular. 



Reptiles are endowed with five senses, but none of 

 them. in great perfection. In those species which are 

 covered with scales or plates, the sense of touch is very 

 obtuse ; and in the species which have a naked skin, such 

 as the frog, it is also weak, in consequence of not being 

 adherent to the body, but invelopes it like a bag. In the 

 serpents, the eyes are immovable, and are destitute of 

 eyelids ; and the eyes covered with a corneous substance ; 

 in some genera, three eyelids are distinguishable, while 

 others are destitute of sight. They have no cochlea, and 

 only provided with a small bone under the tympanum. 

 Their nostrils are small, and they appear to have a very 

 weak sense of smell. They have no delicacy of taste, lor 

 almost all the species swallow their food entire, and those 

 in which the tongue is soft and flexible, this organ serves 

 chiefly as an instrument for the seizure of their food. 

 None of them have true fleshy lips ; and some, such as 

 the tortoises, are provided with a horny bill, like that of 

 a parrot ; others have teeth of various forms, which are 

 not, however, formed for mastication, but to assist in 

 holding their prey: various serpents have hollow fangs, 

 which they can erect at pleasure, when they open their 

 mouths to bite, and these fangs have apertures, from 

 which they inject into the wounds made by them an active 

 and deadly poison. The anal opening in serpents 

 serves for rejected matters, as well as for organs of gen- 

 eration. 



The physical construction of reptiles varies consider- 

 ably in the different orders ; deviating in several essen- 

 tial particulars, to which no general characters will 

 apply. The following is an outline of these particulars. 



I. The Chelonia, or Tortoises, have a heart with two au- 

 ricles, and a ventricle, divided into two unequal cavities, 

 which communicate with each other. The blood from 

 the body is poured into the right auricle, and from the 

 lungs into the left, but both kinds of blood are partially 

 mixed in passing through the ventricle : their body is 

 inveloped by two plates, or bucklers, formed by the ribs 

 and sternum, supported by four feet. The envelope of 

 the body permits no part to project, except the head, 

 neck, tail, and four feet. The upper shield, which is 

 called the carpace, is formed by the ribs, of which there 

 are eight pairs; these are widened and reunited by den- 

 ticulated sutures, and with plates adhering to the 

 annular portion of the dorsal vertebrae, in such a man- 

 ner, that all these parts are deprived of mobility. The 

 lower shell, called the plastron, is formed of pieces, 

 usually nine or ten in number, analogous to a sternum ; 

 and this has been denominated the sternum by the more 

 recent writers on natural history. A frame work, con- 

 sisting of bony pieces, which have been considered as 

 analogous with the cartilaginous portion of the ribs in 

 the mammalia, generally encompasses the upper shell, 

 uniting all the ribs which comprise it. The vertebrae 

 of the neck and tail are alone movable. These two 

 bony envelopes being covered with skin or by scales, the 

 scapula and all the muscles of the arms and neck, in- 

 stead of being articulated to the ribs and spine, as in 

 other animals, are attached beneath ; the same arrange- 

 ment is found in the bones of the pelvis, and also in all 

 the muscles of the thigh, so that in this respect tor- 

 toises have been termed retroverted animals. The ver- 

 tebral extremity of the scapula is articulated with the 

 shield, and the opposite extremity of the clavicle with 

 the breastplate or sternum, in such a manner, that the 

 shoulders form a ring for the passage of the trachea and 

 oesophagus. A third and larger bony branch, is directed 

 downward and backwards, representing the coracoid 

 apophysis in birds. The lungs are extensive, and situated 

 in the same cavity with the other viscera. The thorax 

 being immovable in the greater number, it is by the 

 action of the mouth that the tortoise respires; this pro- 

 cess being effected by keeping the jaws closed, and 

 alternately raising and depressing the os hyoides. The 

 first movement permits the air to enter by the nostrils, 

 and the tongue afterwards closing the interior opening, 

 the second movement forces the air into the lungs. Tor- 

 toises are devoid of teeth; their jaws are invested by a 

 horny covering, similar to the mandibles of birds, ex- 



