MUSCLES OF THE PERINEUM. 221 



expulsion ; by their action the foetus is expelled from the uterus, the 

 urine from the bladder, the faeces from the rectum, the bile from the 

 gall-bladder, the ingesta from the stomach and bowels in vomiting, and 

 the mucous and irritating substances from the bronchial tubes, trachea, 

 and nasal passages, during coughing and sneezing. To produce these 

 efforts they all act together. Their violent and continued action pro- 

 duces hernia ; and, acting spasmodically, they may occasion rupture 

 of the viscera. The quadratus lumborum draws the last rib down- 

 wards, and is an expiratory muscle ; it also serves to bend the verte- 

 bral column to one or the other side. The psoas parvus is a tensor 

 of the iliac fascia, and, taking its fixed origin from below, it may as- 

 sist in flexing the vertebral column forwards. The diaphragm is an 

 inspiratory muscle, and the sole agent in tranquil inspiration. When 

 in action, the muscle is drawn downwards, its plane being rendered ob- 

 lique from the level of the ensiform cartilage, to that of the upper lumbar 

 vertebra. During relaxation it is convex, and encroaches consider- 

 ably on the cavity of the chest, particularly at the sides, where it 

 corresponds with the lungs. It assists the abdominal muscles power- 

 fully in expulsion, every act of that kind being preceded or accom- 

 panied by a deep inspiration. Spasmodic action of the diaphragm 

 produces hiccough and sobbing, and its rapid alternation of contraction 

 and relaxation, combined with laryngeal and facial movements, laugh- 

 ing and crying. 



MUSCLES OF THE PERINEUM. 



The muscles of the perineum are situated in the outlet of the pelvis, 

 and consist of two groups, one of which belongs especially to the 

 organs of generation and urethra, the other to the termination of the 

 alimentary canal. To these may be added the only pair of muscles 

 which is proper to the pelvis, the coccygeus. The muscles of the peri- 

 neal region in the male, are the 



Accelerator urinae, 

 Erector penis, 

 Compressor urethra?, 

 Transversus perinei, 

 Sphincter ani, 

 Levator ani, 

 Coccygeus. 



Dissection. To dissect the perineum, the subject should be fixed 

 in the position for lithotomy, that is, the hands should be bound to 

 the soles of the feet, and the knees kept apart. An easier plan is the 

 drawing of the feet upwards by means of a cord passed through a hook 

 in the ceiling. Both of these plans of preparation have for their 

 object the full exposure of the perineum. And as this is a dissection 



