1874.] MYOLOGY OF PHRYNOSOMA. 81 



Sphincter cloacae (fig. 4, Sp. C). — The fold of skin which forms 

 the posterior boundary of the cloacal aperture encloses a muscular 

 band, which appears to perform the function of a sphincter, although 

 it is not homologous with the sphincter ani ; it arises from the ilio- 

 ischiatic ligament behind the transversus perinei, and then passes 

 behind the cloaca to be inserted on the opposite side in the same 

 manner and at the corresponding place. 



Retractor cloacce (fig. 4, B.C.) arises by two origins from the 

 transverse processes of the sixth and seventh caudal vertebrae, which 

 pass forward and unite together into one muscular fasciculus, the 

 superficial fibres of which are inserted into the posterior border of 

 the last a short distance on the outside of the mid line, while its 

 deeper fibres pass beneath to be inserted into the outer edge of the 

 cloaca ; some of the fibres also spread out over the anterior margin of 

 the same. 



Constrictor cloacce (fig. 4, CO.) arises from the transverse pro- 

 cess of the third caudal vertebra, and is inserted near the apex of the 

 cartilaginous rod which is attached to the posterior end of the sym- 

 physis ischii, above the posterior part of the origin of the trans- 

 versus perinei ; its fibres are attached to the side of the cloaca in 

 their course, so that they are capable of constricting it. 



Intertransversalis caudce (figs. 4 & 5, It. C.) is a muscle which 

 runs along the extremities of the transverse processes of the six 

 anterior caudal vertebrae ; posteriorly it blends with the ordinary 

 caudal muscles ; anteriorly it unites with the under surface of the 

 sacro-lumbalis, and is attached to the posterior end of the ilium. 



Adductor magnus (fig. 4, A.M.) arises by a flat tendon from the 

 ilio-ischiatic ligament beneath the origin of the gracilis, and is inserted 

 fleshy into the internal condyle of the femur and into the interarticular 

 cartilage of the knee-joint. No muscle corresponding to this was 

 found in either P.japonicum or Liolepis belli : neither is it mentioned 

 by Mr. Mivart as occurring in Iguana. There appears to be a muscle 

 somewhat like it in Chamceleon ; but, from the description, I should 

 imagine that it does not extend so far as the condyles. 



Pectineus (fig. 4, Pc.) arises from a point of the ischium behind 

 and internal to the acetabulum, and from the deep surface of the 

 aponeurosis which covers the lower surface of the pubis and ischium. 

 Its origin is a broad expanse of muscular fibre ; it is inserted into the 

 ventral surface of the femur, occupying one fourth of its length on 

 the proximal side of the central point. I am uncertain whether to 

 call this pectineus or an adductor ; the point in favour of its being 

 pectineus is, that its insertion is more towards the ventral surface 

 than would be the case if it corresponded to an adductor. 



Pelvo-tibialis (fig. 4, P.T.) may be described as arising by two 

 heads, one from the anterior division of the flexor femoris, the other 

 from the outer and anterior edge of the pubis, in front and rather to 

 the inside of the origin of the rectus femoris ; each head is an elon- 

 gated narrow muscular ribbon, which proceeds down the thigh ; the 

 two joining together form a short tendon, which penetrates the knee- 

 joint and is attached to the tendon of the semimembranosus, which 

 Proc. Zool. Soc— 1874, No. VI. 6 



