186 7. J MYOLOGY OF IGUANA TUBERCULATA. 789 



physis (figs. 14, 16, 17 & 18, S.). It is slightly connected, at its 

 origin, with the first part of the iUacus, and some fibres spring from 

 the brim of the pelvis just below the tendon of the rectus femoris. 

 Passing downwards between the rectus femoris and the adductor, 

 and passing peronead of the first part of the semimembranosus, it 

 goes very deeply into the popliteal space (between the two heads of 

 the gastrocnemius), and, uniting with the second part of the semi- 

 membranosus, is inserted by a tendon into the peroneal side of the 

 head of the tibia above and behind the insertion of the tendon of 

 the biceps. This muscle is easily separable longitudinally into two 

 parts. 



Semimembranosus. This muscle consists of two portions so distinct 

 in insertion that they may well be considered two separate muscles: — 



(1) The first portion (figs. 14, 15, 17 & 18, S. 31. 1) arises from 

 the tuberosity of the ischium, and from the tendinous arch which 

 passes from the posterior end of the ilium to the spine of the pubis. 

 Its origin is nearly in the same vertical line as, though ventral to, 

 the common origin of the biceps and semitendinosus. Thick and 

 fleshy, it is inserted into the back of the leg, embracing the inner 

 head of the gastrocnemius, some fibres passing beneath the internal 

 lateral ligament, while others extend along the posterior margin of 

 the summit of the tibia. 



(2) The second portion (figs. 15, 17 & 18, 5. M. 2) arises in 

 common with the first portion, and is inserted by a tendon (common 

 to it and to the tibial adductor) into the summit of the peroneal 

 surface of the tibia. 



The semitendinosus (figs. 14, 17 & 18, S. 2\) springs in common 

 with the biceps from the strong tendinous arch just mentioned as 

 passing from the posterior end of the ilium to the spine of the pubis, 

 behind and a little above the tuberosity of the ischium. It is inserted 

 by a strong tendon, common to it and to the gracilis, into the inside 

 of the upper part of the tibia, at the lower end of the internal lateral 

 ligament. The insertion is mainly superficial to the last-mentioned 

 ligament ; but a few tendinous fibres appear to pass inside it. 



Biceps (figs. 15, 17 & IS, B.F.). This arises, in common with 

 the muscle last described, from the strong ligamentous arch passing 

 from the ilium to the spine of the pubis, and arching over the great 

 femoro-caudal tendon. Tt is inserted by a slender tendon, which 

 goes very deeply into the popliteal space (between the two heads of 

 the gastrocnemius), and, passing between the tibia and fibula, is in- 

 serted into quite the anterior aspect of the outer (peroneal) side of 

 the tibia a little below its upper margin and below and in front of 

 the insertion of the tendon common to the second part of the semi- 

 membranosus and the tibial adductor. 



The biceps becomes intimately united with the gastrocnemius, as 

 it gives off a strong tendon (fig. 18), which runs down just internal 

 to the outer border of the iinier head of that muscle. 



Ilio-peroneal (figs. 15, 16, 17 & 18, /. P.). A long and strong 

 muscle, which arises from the posterior part of the outer side of the 

 ilium, covered by the posterior portion of the tendinous origin of the 



