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Show 1874.] MYOLOGY OF PHRYNOSOMA. 81 Sphincter cloaca (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 cloaca (fig. 4, R.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 cloaca (fig. 4, C.C.) arises from the transverse process of the third caudal vertebra, and is inserted near the apex of the cartilaginous rod which is attached to the posterior end of the symphysis ischii, above the posterior part of the origin of the transversus perinei; its fibres are attached to the side of the cloaca in their course, so that they are capable of constricting it. Intertransversalis cauda (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 Chamaleon ; 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 bein°- 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 elongated 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 |
