REPTILES. 



5. The fame kind of motion, produced by the alternate 

 formation and difappcarnnce of folds in the fl<iii of the fides. 



6. Without any undulation, merely by the alternate ap- 

 proximation and feparation of rings of the body. 



Tlie rcpulfivc- motions, by whicli reptiles move their 

 bodies forwards in water, are nearly the fame as they em- 

 ploy in jumping ; but they mull be much quicker. To 

 rife in the water, they muil ilrike back the water below 

 and behind them, and diminifli tiie breadtli of their body, 

 as much as polliblc, by carrying tiieir fwimming organs 

 hackwards after each ilroke. Tluis we fee the frog, after 

 Itriking, extend its long hind legs, fo as to offer no refdt- 

 ance to the paffage of the body tlirougli the liquid. The 

 aCl of fwimming offers the following modifications. I. Ex- 

 ternal fwimming (on tlie furface of the water, breathing 

 air) by vertical undulations, without fwimming organs. 

 The ferpents. 2. The fame by lateral undulations, afliflcd 

 by the feet. Iguauas, lizards, &c. 3. Swimming under 

 the furface, breathing externally ; by four palmated feet, 

 and without tail. Hyla palmata ( Rana maxima, Linn.) 

 4. The fame with four legs and no tail. Frogs properly fo 

 called. 5. The fame with four feet, an elongated body, and 

 depreffed tail. Crocodiles, falamanders. 6. The fame by 

 means of four fin-like icaly members, and no tail. 7. Swim- 

 ining under water, breathing by means of branchise. 



The dragons are the only reptiles capable of flying. 

 Their flight is nearly the fame with that of the polatouche, 

 or flying fquirrel. Daudin, Hift. Nat. des Rept. t. i. 



The Brain. — The brain of reptiles docs not fill more than 

 one-half of their very fmall cranium ; hence its relative 

 fize to that of the body is very inconiiderable. Its pro 

 portion to the body is faid to be, in the tortoife ^ir^-sj '" the 

 turtle ^V.'.^-j '" the coluber natrix y-,i-j-, in the frog -ri-r- 

 Blumcnbach juilly obfervcs, that anatomifls have hitherto 

 bellowed but little labour on the brains of the amphibia. 

 The dura mater forms no procefles in this order ; the inter- 

 val between it and the pia mater is filled with fluid ; the 

 brain is fmall and fimple, and confills of five roundilh emi- 

 nences. Of thefe, the fingle one, placed at the front of 

 tlie uicdulla fpinahs, is clearly the cerebellum, as in all 

 animals which have a nervous fytlem. Whether the four 

 others are to be regarded as the two hemifpheres, and the 

 thalami nervorum opticorum, is more doubtful. According 

 to Blumenbach, the cerebellum does not exhibit the arbor 

 vits. 



All the parts of the brain of reptiles are Imooth, and 

 without circumvolutions. Tile optic thalami are fituated 

 behind the hemifpheres, but are not covered by them. 

 They contain each, as in birds, a cavity 'A'hich communicates 

 with the third ventricle. At tlie extremities of this s^en- 

 tricle, we obferve the anterior and poflerior commiffure, 

 but there is no loft commiflure, nor tubercula quadrige- 

 mina. 



In the tortoife the hemifpheres form an oval. Tiieir 

 anterior part is feparated from the poflerior by a fulciis, 

 and reprefents a kind of bulb, which ferves as a root to 

 the olfaftory nerves. The fize of this bulb is about equal 

 to one-third of the hemifphere. The interior of the hemi- 

 fphere is, as ufual, excavated by a ventricle, and contains a 

 fubllance analogous to the corpus flriatum, and which 

 pretty much refembles in its form that of birds. 



The optic thalami are not larger than the bulbs of the 

 olfadlory nerves. Their form is nearly round. They ex- 

 tend downward and forward, under the hemifpheres, to 

 produce the optic nerve. The valve of the cerebrum is 

 fituated between them and the cerebellum. No tubercle is 



Vol. XXIX. 



either placed above it or before it, aiid. it givei origin, a* 

 ufual, to the fourth pair of nerves. 



Before the optic thalami, and under tUe poflerior part of 

 the hemifpheres, thei'- is a tubercle which corrcfpoiids to 

 that we have remarked in birds. 



The cerebellum is nearly li'-mifpherical. The fourth 

 ventricle penetrates a confiderable way into its fubflance. 



In the frog the hemifpheres are longer and narrower. 

 The optic thalami are larger in proportion to the iiemi- 

 fpheres. Their ventricle is very diflindt. It is the con- 

 trary in falamanders, which have the optic thalami very 

 fmall, and the hemifpheres almoll cylindrical. 



The cerebellum of thefe two kinds of reptiles is flat, 

 triangular, and lies pofleriorly on the medulla oblongata. 



In the ferpents the two iumifpheres form togetiier a mafs 

 which is broader than long. The optic tiialami are almofl 

 round, and one-half Icfs tlian the heinifpheies, behind which 

 they are fituated. The olfaftory nerve has no appaccnt 

 bulb. Tile cerebellum is exceedingly fmall, flat, and in 

 the form of a portion of a circle. 



In all thefe animals the inferior furface of the brain is 

 nearly fmooth. The optic thalami make no proje£lion 

 downward, and the pons Varolii does not exiil. 



Cuvier afligns, as the diltinguifliing charadler of the 

 brain in reptiles, the pofition of the optic thalami behind 

 the hemifpheres. And he flates the following as the points 

 in which reptiles, fifhes, and birds, differ from the mam- 

 malia. The want of corpus callofum, fornix, and their 

 dependencies. Some tubercles, more or fewer, between 

 the corpora ilriata and the optic thalami. The thalami 

 containing ventricles, and being dillinft from the hemi- 

 fpheres. The abfence of any tubercle between the thalami 

 and the cerebellum, as well as the abfence of the pons 

 Varolii. Reptiles and fifhes are diftinguifiied from the 

 mammalia and birds by the want of the arbor vitre. 



The brain of the tortoife has been delineated by Caldefi, 

 oflervazioni intorno alle Tartarughe, tab. 2. fig. 5 : that 

 of the frog by Ludwig, de cinerea cerebri fubftantia ; by 

 Vicq d'.\zyr in the Mem. d'Acad. dcs Sciences, 1783 ; 

 and by Ebel, in his Obfervat. Neurol, ex Anat. Compar. j 

 and that of the viper, by Vicq d' Azyr. 



Origim of the A'lrves. — The olfactory nerves arife, as in 

 birds, from the anterior extremity of the hemifpheres. The 

 optic nerves feem to derive their origin from a common emi- 

 nence, fituated under the middle of the hemifphere. Tlie 

 other neTves exhibit no particularities as to their origin. 



Dyirihution of the Nerves The oifaSory nerve proceeds 



to the noltrils in this clafs nearly in the fame manner as in 

 birds ; but it is longer. The canal w liich receives it is 

 partly oil'eous and partly cartilaginous. The two canals 

 have only one common apertui'e within the cranium. The 

 olLictory nerves of reptiles are generally much more folid 

 than thofe of the preceding claffes. 



The two optic nerves are joined together, as in the mam- 

 malia. There is nothing worthy of remark about the third, 

 fourth, and fixth pairs. 



Reptiles have the three branches of \he fifth pair. In the 

 fea tortoifes the ophthalmic pafles, fome way, in the dura 

 mater before it enters the orbit. It tranfmits filaments to 

 the mufcles of the globe of the eye, and particularly to the 

 two l.ichrymal glands. The fuperior maxillary branch is 

 the largeft of the three. It is united to the inferior branch 

 at its origin, but when it reaches the interior of the orbit, 

 it feparates from it to take another diredlion. It paffes 

 along the floor of the orbit, defcribing a very marked cur- 

 vature, the convexity of which is external. A very great 

 number of filaments proceed from the concave or internal 

 5 E fide, 



