. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 488 COMPARATIVE ANATOMY the proximal end of which the vasa deferentia open. In Crocodiles the free portion is relatively longer and the groove deeper than in Chelonians. In many Birds a copulatory organ is present, formed on a similar plan to that of Crocodiles. It is well developed amongst the Ratitae and Lamellirostres, and in many other Birds can be recognised in a rudimentary condition. In Struthio it resembles that of the Crocodile, except that the distal free portion is longer; it is grooved above, encloses cavernou
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 488 COMPARATIVE ANATOMY the proximal end of which the vasa deferentia open. In Crocodiles the free portion is relatively longer and the groove deeper than in Chelonians. In many Birds a copulatory organ is present, formed on a similar plan to that of Crocodiles. It is well developed amongst the Ratitae and Lamellirostres, and in many other Birds can be recognised in a rudimentary condition. In Struthio it resembles that of the Crocodile, except that the distal free portion is longer; it is grooved above, encloses cavernous tissues, and is supported by a fibrous body, bifurcated at the base. In Dromseus and Rhea there is an aperture at the apex of the penis leading into an elongated and curved blind sac, in which is a furrow, lined by cavernous tissue, continuous with the groove on the dorsal side of the organ. In the Duck and Swan the spiral penis is essentially similar to that of Dromseus and Rhea. The absence of the blind sac in the Ostrich is probably a secondary modification. A clitoris is present in the female of the above-mentioned Birds. The penis of Monotremes may be best understood by imagining a hypothetical form intermediate between it and that of. FIG. 367.—TRANSVERSE SECTION OF THE CLOACA OF A CHELONIAN. Slightly diagrammatic. (After Boas.) "it— ;'. fibrous body: r, seminal furrow, bounded by cavernous -issue; r, wall of cloaca. ^ Crocodiles and Chelonians (Figs. 368, B). We must suppose that a sac-like outgrowth into which the ureters and vasa deferentia open has become developed from the ventral cloacal wall at the base of the penis, the groove in which has become converted into a canal. The Monotreme condition is reached by the sac elongating to form a urinogenital canal, into the distal end of which the urinary and genital ducts and the bladder open (c, D). The penis consists of an unpaired fibrous body enclosing the seminal canal, and is only loosely surrounded by the
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