The crural-ischial plexuses (Fig. 32) are made up of branches from five nerves, three presacral (a, b, and c), the sacral (s = xxvi), and one postsacral (α); the second postsacral shown in the figure apparently does not enter into the plexus. The first and second presacrals terminate chiefly in the abdominal and thigh muscles, though the second sends a large branch to fuse with a branch from the third to form the large obturator nerve (N. obt.) that leads to the muscles of the thigh and knee. The third presacral sends a branch back to fuse with the large sacral (s = xxvi), and these two, together with a branch from the first postsacral, form a complicated network that sends numerous branches to the muscles of the pelvic and femoral regions, to the skin, legs, and tail, as shown in Figure 32. The large muscles of the tail are innervated by the regular, metameric nerves of that region, and since there are usually thirty-nine caudal vertebræ, there are probably about that many pairs of caudal nerves, although the last few vertebræ and the muscles of that region are so small it may be that some of the nerves are lacking. SPECIAL SENSE ORGANS It is not possible in a work of this size to give much space to the discussion of the anatomy of the special sense organs. A few of the main features will be given here, taken mainly from Bronn’s _Thierreich_, but for details of structure the reader is referred to that larger work. _The Eye._ As might be expected, the Crocodilia have the usual upper and lower eyelids and the nictitating membrane. Except along their thickened rims the lids are usually rather faintly pigmented, and near the thickened border numerous goblet cells are found. The structure of the upper and lower _lids_ is similar except that in the former a bony formation is present, as a support to that lid, even in very young animals. The arrangement of the muscles, which are of both smooth and striped fibers, and the histological structure cannot be described here. The _nictitating membrane_ is strongly developed in the Crocodilia. Its outer surface is marked by two fairly high folds that are conspicuously pigmented. The cartilage described in the nictitating membrane of Lacerta is wanting, according to Bronn, in the Crocodilia. The glands of the eye are of three types: the lachrymal glands proper, the Harderian glands, and the conjunctival glands. The _lachrymal gland_ is small in proportion to the size of the eye. It is an elongated, almost band-like structure situated in the roof of the eye-socket, near its border; its long axis lies in an antero-posterior direction. It is so closely inclosed by and united with connective tissue that it is difficult to find.