The Vascular System 



213 



7»<7 



arches arises the most anterior of seven or eight 

 pairs of lumbar 

 arteries, lu 1-7; 

 this first lumbar 

 artery is contin- 

 ued cephalad for 

 some distance as 

 a longitudinal 

 trunk that gives 

 off several lateral 

 branches to the 

 walls of the thor- 

 acic region. The 

 other six or seven 

 lumbars are dis- 

 tributed to the 

 dorsal body wall, 

 and arise, at 

 more or less reg- 

 ular intervals, as 

 far caudad as the 

 sacrum, or even 

 back of that 

 point. 



The first large 

 branch of the 

 aorta is the un- 

 paired mesen- 

 teric artery, m^ which is given off in about 

 the region of the fourth pair of lumbars; it 



Fig. 61. The arteries of the posterior 

 region of the Florida alligator. — For lettering, 

 see pages 224-25. 



