Remarks on the cloaca and on the copulatory organs of the Amniota / by Hans Gadow.

  • Gadow, Hans Friedrich, 1855-1928.
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: Remarks on the cloaca and on the copulatory organs of the Amniota / by Hans Gadow. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    fibres on to the caudal end of the Symphysis ischii and to the neighbouring corner of the anal opening. Contraction of this muscle opens the anus. The side walls of the anal portion of the cloaca are surrounded by a rather thin layer of muscles, which arise in the median line between the right and left halves of the M. ischio-caudalis, from some of the first chevron bones of the caudal vertebrae. Their fibres are directed more or less transversely towards the margin of the anus, where they are attached. The most superficial portion of this system has, however, a more longitudinal direction and is somewhat differentiated off from the rest; its fibres meet at the anterior corner of the anus and surround the latter like a sphincter. Their contraction closes and elongates the anal slit, whilst through the action of the more transverse, deeper mass the anal walls are drawn inwards and are thus likewise closed. All these muscles, viz., the M. transversus perinei, s. ti'ansversus latei’alis, s. levator, and the M. transversus medianua, s. sphincter, together with the M. rectus lateralis, are supplied by a strong branch of the ischiadic plexus. In Alligator toississipieifsis this nerve-branch comes from the stem a, i.e., the first postsacral spinal nerve. It leaves the pelvis laterally from the tendinous insertion of the M. ischio- caudalis, between this tendon and the posterior margin of the ischium near the symphysis, and then it supplies, situated superficially, the muscles, sending out at the same time cutaneous branches. Considering the nerve-supply, it seems more reasonable to suppose that the sphincter muscles are, at least' in the Crocodilia, a differentiation of the post-pelvic portion of the system of the M. rectus abdominis, and not of the true caudal muscles. In the Chelonia the penis is not attached to the pelvis, nor is it in connexion with any anal muscles ; but to its dorsum, not far from the glans, are attached a pair of long retractor muscles, which pass laterally from the M. pubi-caudalis (fig. 10) (flexor caudae obturatorius, Bojanus) into the pelvis, and arise from one of the most anterior lumbar vertebrae. The position and nerve-supply of these peculiar muscles show that they are differentiated from the MM. lumbo-cauclales (flex, caudae lumbales, Bojanus). There is consequently no homology whatever between this Chelonian retractor (sometimes called M. ischio-cavernosus) and any of the Avian and Mamma- lian copulatory muscles. Its function is somewhat complicated. When the penis is erected and protruded, the muscle acts as the retractor, but when the organ is in a relaxed condition and, when at rest, doubled up and withdrawn into the cloaca, as shown in fig. 26, contraction of the muscle, owing to its pulley-like course round the M. pubi-caudalis, undoubles it and protrudes it so far that the glans becomes visible in the anal opening. This is seen in micturating Tortoises, because the penis has to be straightened in order to withdraw the glans from its position ventrally from the fold p, where it blocks the opening of the bladder. During defiecation, on the other hand, the doubled halves of the penis are pressed against each other, and, together with the fold p, which is likewise pressed down, effectively protect the urino-genital