PLEXUS AND SACRAL VERTEBRAE OF LIZARDS. 519 



(16) to the iliacus, then continues on to he distributed to the crureus (20) and rectus 

 femoris (19), giving off in its course branches to the (so-called) gluteus meclius (17) and 

 maximus 1 (18). 



The first presacral nerve (21), which is the largest of all, goes entirely to join the 

 postaxially extending bifurcation (12) of the second presacral nerve already mentioned ; 

 and these then, having effected a junction, are continued on by a single trunk (22) to 

 join the intersacral nerve (29). 



The intersacral nerve (29) gives off, in the male, very close to its root, a very small 

 branch (31) to the penis, and then receives accessions, in the shape of two slender 

 branches (32 and 32), from the first postsacral nerve (30). The intersacral nerve, before 

 joining the conjoined trunk formed by the two more preaxial nerves, may give off a 

 branch (36 a) to the femoro-caudal muscle 2 , or a branch to this muscle may be given 

 off (36) from the great sciatic nerve itself. 



The three roots of the sacral plexus (the intersacral and two presacrals) having thus 

 joined into one whole mass, the said mass divides into three unequal branches. The 

 smallest of these branches bifurcates and goes to the obturator internus 3 muscle (23). 

 A second branch, which is rather slender, curves round the tendon of the femoro-caudal, 

 and gives off branches to the gracilis (24), the semimembranosus (25), the semitendinosus 

 (27), and the pyriformis (28) and biceps femoris muscles. 



The main branch from the sacral plexus, the great sciatic nerve (33), gives off three 

 small branches to the gluteus medius (34) and maxim/as, to the ilio-peroneal (35), and to 

 the femoro-caudal (36) muscles. It then continues on down the thigh, just where the 

 deep edges of the gluteus maximus and ilio-peroneal are adjacent to each other, and, 

 distally, close to the delicate tendon of the femoro-caudal muscle 4 . When about two 

 thirds down the thigh, the sciatic nerve divides into the internal (37) and external (38) 

 popliteal; and later the latter again divides into two branches (39 and 40). 



The first postsacral nerve (30), much smaller than the three preceding nerves, very 

 soon gives off a very long branch (44), which descends into the femoro-caudal muscle 

 and passes down the tail. It then bifurcates, but before or after bifurcating supplies 

 the slender branches (32 and 32) before mentioned which go to the intersacral nerve. 

 Its preaxial bifurcation ends by small branches (45), which supply the skin, transversus 

 perinei, and external, lateral, and caudal muscles. Its postaxial bifurcation (41) passes 

 under the tendon 5 from the caudal muscles which is attached to the tuberosity of the 

 ischium. It becomes connected by a very short branch (41 a) with the second postsacral 

 nerve, and then ends in delicate branches, which go to the external skin, transversus 

 perinei 8 and sphincter cloaca? muscles. 



The second postsacral nerve (42), more delicate than the first, gives off a branch (43) 



1 This muscle is described at p. 791 of the paper referred to. Therein doubt was expressed as to correct naming 

 of the muscle, the name of which was chosen from the resemblance of the muscle in question to the gluteus maximus 

 of the Echidna. Its nervous supply coming from the crural, is a strong argument against its being really the gluteus 

 maximus. 2 For this muscle see p. 794 of the paper before referred to. 



3 See I. e. p. 793. 4 For this tendon see I. c. p. 79-1, figs. 17 & 18 y. 



5 See I. c. p. 774. 6 See l c. p. 773. 



3z 2 



