REPTILES. 



orbicular gland, placed in front of the bafe of the heart, 

 likewiff to another gland of a more confulerable fize and 

 elongated form, fituate beneath the jug'jlar. Tlie trunk 

 then furnifhes the common carotid, the only one cxi(tin;f 

 in this order of reptiles. It paffes obliquely to the left, 

 and advances, by the fide of the left jugular, between the 

 trachea and the cefophagus, and lallly beneath the latter. 

 It fends a great number of ramifications to thefe organs, 

 and divides near the head into many branches diftributed 

 to the adjacent parts. Near to the vertebral column, 

 the right aorta produces a confiderable branch correfpond- 

 ing to the vertebrals and fupcrior intercollals which pro- 

 ceeds along the fpine, fending to it branches, and wholly 

 penetrating into it near the head. When the commu- 

 nication takes place between the right and left aorta, the 

 diameter of the former is become very fmall, fo that the 

 p-reatell part of the blood which it has received from the 

 heart is diftributed to the parts in front of that vifcus : it 

 is properly the anterior aorta. The left aorta afcends and 

 turns backwards to the left, pail'es beneath the oefophagus ; 

 then by the fide of and always beneath the lung, receiving 

 the right aorta beyond the heart ; and continuing to pafs in 

 a diredion backwards, it gives off branches correfponding 

 to the intercoftals, likewife arteries to the vifcera. Thole 

 branches proceeding to the ftomach, pulmonary bladder, and 

 liver, are detached fucceflively from the aorta, as it pro- 

 ceeds backwards ; thus there is no caeliac trunk. Nearly 

 oppofite to the pylorus, the aorta furnifties the anterior 

 mefentcric, which proceeds parallel to the inteltinal canal 

 one half of its extent, fending to it branches. Farther 

 backwards the inteftinal canal receives three other fmall 

 branches in fucceffion, from the fame artery : as it pafl'es 

 backwards, it alfo fends finiilar branches to the kidnies, 

 ovaries, &c. ; arrived at the lower part of the abdomen, it 

 penetrates beneath the vertebrae of the tail and is lolt in that 

 part. 



In the lafl order of reptiles, the Batracians, the aorta, 

 which proceeds from the bafe of the ventricle, foon divides 

 into two branches, which feparate and purfue a very oblique 

 direftion from within, outwards and a little forwards. Each 

 branch gives off a pulmonary artery, a common carotid, 

 an axillary, a vertebral, and arteries correfponding to the 

 intercoftals ; then turning backwards, and approaching its 

 fellow, it fpeedily, becomes united to it. The trunk formed 

 by their junftion gives off^, firft, the cseliac trunk, then all 

 the other arteries which arife ordinarily from the abdominal 

 aorta, prefenting nothing worthy of remark. 



Of the Veins. — In the Chelonians there are two pofterior 

 venx cavse, which pafs through the liver on each fide, and 

 receive in their courfe numerous fmall hepatic veins. Im- 

 mediately after their exit from the liver, they are joined by 

 two anterior venae cavas, one on each fide, or by the com- 

 mon trunk of the jugular and fubclavian. They all ter- 

 minate in the right auricle by an opening in the form of a 

 fiffure, provided with two valves ; they do not terminate 

 in the cavity of the auricle, but in a receptacle communi- 

 cating with it. The pulmonary veins united in a fingle 

 trunk terminate in an analogous receptacle, which opens 

 into the left auricle ; around the borders of the opening, 

 there is placed a flefhy valve in the form of a half moon. 



In the Saurians and Ophidians, there is but one pofterior 

 vena cava, and two anterior, that belonging to the left 

 fide pafles acrofs,. and above the heart, in a diredion from 

 left to right, and terminates in the common receptacle by 

 the fide of the pofterior vena cava. This receptacle, fimi- 

 lar to that found in the chelonians, has in the fame manner 

 its entrance into the right auricle, in the form of a fiffure. 



and provided with two valves. In this order, likewife, the 

 anterior vena; cava; are more properly confidered as the 

 jugulars. Tiiey have alfo a double azygos, one formed by 

 the intercoftal veins in front of the heart, the other pof- 

 terior to it. They both join the right auricle by the fide 

 ot the right jugular. It appears that they are rendered 

 neceffary by the fituation of the venx cavae, which is very 

 remote from the vertebral column, and mi/re inferiorly. 



The pulmonary veins in the faurians are fimilar to thofe 

 of the chelonians. 



In the ophidian order there is only one, which terminate* 

 in the fame manner in the left auricle. Its volume exceeds 

 that of the artery, which we have not obferved in the 

 other reptiles. 



In the batracians the veins have a diftribution fimilar to 

 that of the arteries which refults from their terminating 

 in a fingle auricle, in the fame way as the latter arife from 

 a fingle ventricle. There are two anterior venae cavae 

 which receive the blood from the head, neck, anterior ex- 

 tremities, and from the veins analogous to the external 

 mammary, which are very confiderable, extending beneath 

 the licin to the groins, and likewife a pofterior vena cava, 

 which receives the veins from the other parts, prefenting 

 nothing worthy obfervation. 



The blood-veflels of the tadpole are defcribed in the ac- 

 count of that creature in the divifion concerning the gene- 

 rative fundions ; and thofe of the proteus and firen, in 

 the feparate defcription of thofe animals at the end of this 

 article. 



Phyjwlogy of the Circulating Organs. — The nature of the 

 blood in reptiles, the points in which it differs from the cor- 

 refponding fluid in other claflcs, its difference in the various 

 orders and genera, its relations to the food and to the fecre- 

 tions and excretions, are fo many interefting topics of 

 inquiry, on which we have abfolutely no information to 

 offer. Chemiftry does not yet appear to be fufficiently ad- 

 vanced for the fuccefsful inveftigation of thefe and fimilar 

 matters. 



We may obferve, in the firft place, that the reptiles of 

 thefe climates at leaft, poffefs, in comparifon with warm- 

 blooded animals, a much fmaller quantity of blood in pro- 

 portion to their fize : hence their mufcles are whiter, and 

 fome of their vifcera, particularly the lungs, which are 

 loaded and gorged with fuch a profufion or blood in the 

 warm animals, prefent in this refpeft an appearance alto- 

 gether contrary in reptiles. 



" I made an experiment," fays Blumenbach, " on the water 

 falamander, (lacerta lacuftris, L.) of which I difleded 

 twenty-four, adult, lively, recently taken in the early fpring, 

 and weighing together i^ ounce, in order to meafure the 

 quantity of blood they contained : I could preferve from 

 the whole of the bodies of all, only two fcruples and a half. 

 This fmall quantity of blood is to the whole body as 2^ to 

 36 ; while in an adult and healthy man the proportions are 

 calculated at I to 5. Haffelquift obferved the fame circum- 

 ftance pf the fmall quantit/ of blood in , proportion to the 

 body, in the crocodile of the Nile." Voyage dans le Le- 

 vant & en Paleftine. 



It is alfo remarkable, that the arterial blood of our rep- 

 tiles differs in external appearance in the fmalleft degree, if 

 at all, from the venous, fo that one can be diftinguilhed 

 from the other only by the fituation and courfe of the vef- 

 fels ; while, on the contrary, the bright fcarlet arterial 

 blood of the mainmalia offers fo remarkable a contraft to the 

 dark livid or purple venous fluid ; unlefs when they have 

 been for fome time in a warm bath or other warm medium, 

 when it appears from the elegant experiments of Dr. Craw- 

 7 ford, 



