The muscle of the right side is covered, on almost its entire inner surface (from its hinder end to the liver) by the belly-like skin, and is fairly closely united with it. The left muscle, on the other hand, is only covered by this skin from the hinder border of the stomach forwards; farther forward it lies immediately on the under and left side of the stomach and is united with it by loose connective-tissue. Outwardly both muscles are united by a thin layer of connective-tissue to the true abdominal muscles. So far as yet known this muscle is not present in other reptiles. MUSCLES OF THE POSTERIOR APPENDAGES _Ambiens_ (Plate III., Figs. 1 and 2, amb, Plate IV., Figs. 2 and 4, amb, Plate V., Figs. 2 and 3, amb) (Part I., Rectus femoris and Sartorius partim, Vastus internus, Innere Streckmuskelmasse) (Part II., Gracilis, Rectus femoris, Sartorius). Arises by a short tendon from the anterior spine of the ilium, near its union with the pubis. The muscle swells quickly to a thick belly which, lying under the skin on the forward and inner side of the upper thigh, is again reduced to a small, flat tendon which extends abruptly over the anteromedial surface of the knee joint to its outer side; it then passes through the complex of tendons of the femoro-tibialis muscle, beneath which it unites with the tendon of origin for the peroneus posterior muscle. To this muscle is the following strange muscle to be ascribed (Part II): it springs, small in extent, from the inner surface of the os pubis near the acetabulum, extends thence forward around the pubis, and runs into a long, thin tendon which unites with the insertion tendon of the subcutaneous extensor ilio-tibialis muscle. _Extensor Ilio-tibialis_ (Plate III., Fig. 2, ex. il. tb.) (Part I., Rectus femoris, Adductor flexor, Glutæus maximus; M. du facia lata, Vastus externus, Tensor faciæ latæ, Tensor femoris vaginæ, Glutæus minimus, Tensor faciæ femoris). This muscle, in the Crocodilia, consists of two parts: I. The chief part is long and broad, and springs as a tendon from more than the anterior half of the lateral border of the dorsal crest of the ilium, covering the origin of the ilio-fibularis muscle. Its insertion, by a broad, flat tendon, overlying the femoro-tibialis muscle, together with the tendon of this muscle, is on the anterior surface of the head of the tibia. II. The second, significantly smaller and narrower, part arises outside of the quadratus lumborum by a short tendon from the most dorsal end of the ilium; it goes over, medially, along the nearer head of the ambiens muscle, then to the anteromedial side of the upper leg, into the deeper-lying femoro-tibialis muscle.