IIEPTILES. 



fame fide, and oppofitc to it the primitive iliac of the right 

 fide. Between the two latter arofe the artery of the tail, 

 correfponding to the middle facral artery. The branches 

 of the internal iliacs are very aiialog;ous to tiie fame arteries 

 in mammalia. The trunk divides into two brandies ; one 

 fending branches to the bladder and cloaca ; the other dip- 

 ping into the pelvis, and correfponding to the ifchiatic and 

 poilerior iliac arteries. The external iliac proceeds for- 

 wards upon the border of the pelvis, furnidies an analogous 

 branch to the epigailric, from which arifcs the anterior 

 iliac. The firft deicends upon the internal and inferior 

 parietes of the upper fliell, and pali'eu in a direction from 

 behind, forwards. A fecond branch, which arifes from the 

 external iliac, oppolite to the epigailric, defcends along the 

 anterior border ot the pelvis, as far as thg fymphifis of the 

 pubis, and is loll in the mufcles of that part. After having 

 furniflied thefe two arteries, the external iliac paffes out of 

 the pelvis, takes the name of crural artery, giving off firit 

 the circumflex arteries, then the profunda, and in the refl 

 of its courfe is analogous to what it is found in mammalia. 



The diltribution of the principal arterial trunks in the 

 faurians differs but little from that which has been defcribed 

 in the preceding orders. 



In the crocodile there are three arterial trunks, each hav- 

 ing a didinft opeiting in the ventricle, provided with two 

 femi-lunar valves. The pulmonary artery, which arifes 

 from the cavity bearing the fame nan\c, is fituate to the left, 

 and fomcwhat fuperiorly ; the poilerior left aorta, which 

 arifes from the right and inferior cavity, and is fituate be- 

 tween the pulmonary trunk and the next to be mentioned ; 

 the poilerior right aorta, correfponding to the fupcrior 

 cavity. Thefe three trunks are connefted together for a 

 lliort dillance from their origin. From the latter proceed. 

 In the firft place, the trunk common to the fubclavian and 

 left carotid, which remains attached for fome extent to the 

 poilerior left aorta, then advances obliquely forwards, 

 palles beneath the bronchns, and divides beyond that canal. 

 Secondly, a fimilar trunk for the fame arteries on the right 

 fide. The poilerior aorta, after having given off thefe 

 branches, turns in a diredlion, firll from below upwards, 

 then from before backwards, and divides in a direction ob- 

 liquely inwards beneath the fpnial column, without furnifh- 

 ing any remarkable branch until it receives the communi- 

 cating branch from the left aorta. This latter turns around 

 the bronchus on its own fide, and paffes backwr.rds and in- 

 wards in the fame way as the preceding. After having 

 palled the cardia, it divides into many branches, which 

 proceed to the llomach, fpleen, pancreas, and duodenum. 

 Thefe receive the greateft part of the blood of the trunk. 

 The latter haa no communication with the right aorta, but 

 by an artery, the diameter of which is fcarcely equal to a 

 fourth part of the trunk from which it proceeds. 



We have already alluded to the confequences refulting 

 from this arrangement of the arteries, in the defcription of 

 the heart. All the other arteries derived ordinarily from 

 the abdominal aorta, with the exception of the csliac 

 trunk, here take their origin from the right poilerior aorta. 

 It is remarkable that the anterior mefenteric takes its origin 

 at a very confiderable diftance from the casliac trunk, or 

 from the arteries ordinarily compofing it ; while, in the 

 chelonians, it moft frequently ariles very near, or is even a 

 .branch derived from it. The fplenic is alfo given off by 

 the caeliac. After having paflcd through the fubllance of 

 the fpleen, from its anterior to its poilerior part, and diftri- 

 buted to its fubftance many fmail brandies which arife at a 

 right angle from the trunk, it paffes out almofl as lai-ge as 

 at its entrance, and proceeds to be dillribjited to the rec- 



tum, and the termination of the fmall intefline ; that branch 

 of the fplenic having the latter diltribution, forma a con- 

 fiderable communication with the anterior mefenteric. 



The pulmonary artery, very foon after its origin, divides 

 into two branches, which proceed to the lungs, in the fame 

 manner as m the chelonians. Their diameter is nearly equal 

 to that of the trunks formed by tiie carotids and fubclavians 

 on each fide. 



In the common iguana, which has the heart placed very- 

 far forwards in the chelt, the arteries of the body have, in 

 the fame manner, two diflinft trunks arifing from the two 

 cavities of the heart, although they are united at their 

 origni. The left pofterior aorta does not furnifli any branch 

 before it becomes united to the right. The latter gives 

 origin to the carotids and fubclavians, as in the crocodiles ; 

 but with this dift'erence, that the latter do not arife from the 

 fame part as the former, but much farther backwards, on 

 account of the heart being placed fo much anteriorly. 



In the lizards properly fo called, the two aortae advance 

 forwards out of tiie cliell ; the right having firll divided 

 mto three branches, the left without forming any divifion. 

 The latter turns backwards upon the fides of the neck, to 

 proceed afterwards along the vertebral column ; and at the 

 point where it takes a diredlion from before backwards, it 

 receives the left branch of the right aorta, which forms a 

 curvature in front of it. From its convexity arifes the left 

 carotid. The two other branches of the right aorta turn 

 backwards, and unite in the fame manner on the right fide 

 of the neck, forming two arches in front of each other. 

 The carotid of the fame fide arifes in a fimilar manner from 

 tiie anterior arch, formed by the middle branch. The fub- 

 clavians arife from each aorta a little before their jundlion. 

 We have feen that in the crocodiles and the common iguana, 

 they are produced both by the right aorta. The trunk 

 formed by the union of the two arteries, which unite 

 fpeedily after their origin from the heart, produces the dif- 

 ferent pairs of intercoftal arteries in fucceffion. It gives off, 

 near its commencemejit, an artery to the cefophagus ; far- 

 ther on, a fmall artery which proceeds to the liver ; and ftill 

 farther, an artery which quickly divides into two branches; 

 the anterior of which diilributes its ramifications to the 

 ftomach, fpleen, pancreas, and duodenum. The pofterior 

 belonging to the inteftinal canal is properly the anterior me- 

 fenteric. From the trunk the following arteries next pro- 

 ceed : the lumbar, the fpermatics, the pofterior mefenteric, 

 which proceeds immediately to the redtum, the renal, which 

 are among the laft given off, fince the kidniesare fituate very 

 far back in the abdominal cavity. Laftly, it produces the 

 iliacs and middle facral artery. The latter k of fo confider- 

 able a fize, that it may be regarded as a continuation of the 

 aortic trunk, of which the iliacs appear only as branches. 

 This circumllance evidently depends on the great fize of the 

 tail, in comparifon with the extremities. 



The diflrlbiUion of the prinripal arterial trunks in the third order 

 of reptiles, the Ophidians, becomes much fimplified from the 

 deficiency of extremities, and there being but a fingle lung. 

 The number of the trunks is the lame ; the relations be- 

 tween their openings in the heart have been already men- 

 tioned in the defcription of that organ. The pulmonary 

 artery afcends and turns backwards upon the bafe of the 

 heart, and fpeedily arrives at th« inferior furface of the 

 lung, where it palfes from before, backwards to the left 

 of the vein. The right aorta afcends on tlie fame fide, 

 bends backwards, paffes above the cefophagus, and obliquely 

 backwards and inwards, to join itfelf to the left aorta, 

 fome diftance beyond the point of the heart. It gives off, 

 near its origin, fome Iraall arteries, which proceed to an 



orbicular 



