The base of the penis is attached to the pubis near its symphysis. With this base the most anterior part of the strong ring-muscle of the cloaca is closely attached by a fairly large mass of fibrous tissue. Rathke fails to find any muscles that are concerned alone with the copulatory organs.
In the copulation of the crocodile, according to Rathke, the penis is erected, though how this is caused is difficult to say since the corpora cavernosa consist only of fibrous tissue and the cavernous tissue lining the groove is very thin. The penis can, therefore, project only a short distance from the cloaca. The cavernous tissue is capable of causing only a slight elongation of the shaft, but the glans is considerably elongated by the strong influx of blood into that structure. According to Voeltzkow ([78]) the penis in the Madagascar crocodile is 20 cm. in length.
The clitoris of the sexually mature female crocodile is very much smaller than the penis of a male of the same size, but, according to Rathke, it varies greatly in size in different species. It is built on exactly the same plan as the penis.
According to Bronn the clitoris as well as the penis projects from the cloaca, out through the anus, in the embryo of the crocodile; this was not observed by the present writer in the embryo of the Florida alligator, A. mississippiensis.
CHAPTER VII
THE RESPIRATORY ORGANS
The Larynx and Trachea. In the Crocodilia the framework of the larynx consists of three cartilages, of which two represent the arytenoids of the Mammalia; the third represents the thyroid and cricoid of mammals. The last is considerably larger than the first and is a broad closed ring, differing in form in the different species. In spite of the fact that some of them have a voice, the vocal cords, according to Bronn, are wanting in the Crocodilia. According to Henle the vocal apparatus is produced by the projection into the laryngeal cavity of the inner border of the small arytenoid cartilages and by the infolding, under these cartilages, of the mucous membrane of the larynx; this forms the thick but fairly free folds that, when the glottis is narrowed, are well adapted to produce the harsh tone of the animal.
The epiglottis is absent in the Crocodilia.
In many Crocodilia (C. vulgaris, for example) the trachea, [Fig. 57], tr, forms a loop which begins in some species before hatching, in other species not until long after hatching. In the genus Alligator the trachea is straight.
More universal than this looped structure there is found another peculiar structure in the crocodilian trachea. It is a short vertical partition in the stem just before its division into the two branches. This partition is partly membranous and possesses one or more stiffening cartilaginous strands which are outgrowths of so many cartilaginous rings of the trachea. The number of the stiffening fibers varies in the different species.
