Posterior superior iliac spine Cut end of rectum Apex of sacrum Great sciatic notch Ureter Peritoneum Spine of ischium Bladder wall Seminal vesicle Tuberosity of ischium Ischio-rectal fossa Cut end of rectum External sphincter ani Gluteus maximus better seen in young the prostate the urethra runs more forward for about threequarters of an inch, lying between the two layers of the triangular From C. S.
The iris contains a sphincter and a dilator muscle; the former, supplied by branches from the oculomotorius nerve, is under control of the will, whilst the dilator fibres belong to the sympathetic system.
Didelphia, the alternative name of the group was given in allusion to the circumstance that the uterus has two separate openings; while other features are the inclusion of the openings of the alimentary canal and the urino-genital sinus in a common sphincter muscle, and the position of the scrotum in advance of the penis.
The third or outermost chamber, the proctodaeum, is closed externally by the sphincter ani; the orifice is quite circular.
The hind-gut is also provided with sphincter and dilator muscles, and these may produce rhythmic expansion and contraction, causing an inflow and outflow of water through the anus, which has been supposed to aid in respiration.
This can be experimentally shown - by the method of exclusion - to be caused by a paralysis of the terminals of the third cranial nerve in the sphincter pupillae of the iris.
Striped muscles possessing an autochthonous tonus appear to be the various sphincter muscles.
Besides the sphincter pupillae, the fibres of the ciliary muscle are stimulated.