Anatomy of the cavernous muscles of the kangaroo penis highlights marsupial–placental dichotomy

Abstract

The mammalian penis is a complex hydraulic organ of cavernous (spongy) tissue supported by both smooth and skeletal muscle structures. In placental mammals, the paired Musculus ischiocavernosi anchor the corpora cavernosa to the pelvis (at the ischium), and the paired M. bulbospongiosi converge as they envelop the base of the corpus spongiosum. Male marsupials have a dramatically different anatomy, however, in which both sets of paired muscles remain separate, have a bulbous, globular shape and do not have any direct connection to the pelvis. Here we provide the first detailed anatomical investigation of the muscles of the penis in the western grey kangaroo (Macropus fuliginosus) incorporating dissection, histology, vascular casting and computed tomography. The M. ischiocavernosus and M. bulbospongiosus form massive, multipennate bodies of skeletal muscle surrounding the paired roots of the corpus cavernosum and corpus spongiosum, respectively. Bilateral vascular supply is via both the artery of the penis and the ventral perineal artery. Histological examination reveals cavernous tissues with substantial smooth muscle supported by fibroelastic trabeculae, surrounded by the thick collagenous tunica albuginea. The M. ischiocavernosus and M. bulbospongiosus are known to function during erection of the penis and ejaculation via muscular contraction increasing blood pressure within cavernous vascular tissues. The thick muscular anatomy of the kangaroo would be well suited to this function. The absence of any connection to the bony pelvis in marsupials suggests the possibility of different mechanisms of action of these muscles with regard to reduction of venous return, eversion from the cloaca, or movements such as penile flips, which have been described in some placental mammals. This highlights a greater diversity in form and function in the evolution of the mammalian penis than has been previously considered.

Comparative study between Mathieu repair and Snodgrass repair in distal hypospadias

“…[6] Anterior hypospadias constitutes 71%, middle 16%, and posterior 13% [7]. Between congenital anomalies, hypospadias is unique as it has different surgical techniques for the treatment of a single condition [8] . The object of therapy is to reconstruct a straight penis with a meatus as close as possible to the normal site [ventrum of the terminal aspect of the glans] to allow a forwarddirected urine stream and normal coitus.…”

Morfometri Organ Reproduksi Pademelon Kelam (Thylogale brunii) Jantan

“…Hasil ini berbeda dengan hasil penelitian Paris et al (2005), dan bobot crus penis memiliki korelasi yang nyata terhadap berat tubuh wallaby Tammar dan meningkat drastis ketika musim kawin tiba. Pada kanguru kelam barat (Macropus ischiocavernosi), teradapat struktur yang massif dan multipennate dalam kaitannya dengan bobot crus penis (Warburton et al, 2019).…”

Spicules and skeletons: mantle musculature of two species of dorid nudibranchs (Gastropoda: Nudibranchia: Doridina)

“…The relative proportion of hemoceolic space to musculature varies among hydrostatic skeletons (Kier 1988) and less fluid-filled space generally means finer, but slower, control of movement (Kier 2012). Other trabecular fibre networks are found in the mammalian penis, eye and subarachnoid space, and may play a role in mechanical resilience and fluid flow (Tamm 2009;Mortazavi et al 2018;Warburton et al 2019). As another possible explanation, tissue from some caryophyllid-bearing dorids tears more easily than Cadlina mantle (B. Penney, pers.…”