MUSCLES OF THE PERINEUM. 219 



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

 these efforts they all act together. Their violent and continued action 

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

 of the viscera. The quadratus lumborum draws the last rib downwards, 

 and is an expiratory muscle ; it also serves to bend the vertebral 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 assist in flexing the verte- 

 bral 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 oblique from the level of the ensi- 

 form cartilage, to that of the upper lumbar vertebra. During relaxation 

 it is convex, and encroaches considerably on the cavity of the chest, par- 

 ticularly at the sides, where it corresponds with the lungs. It assists the 

 abdominal muscles powerfully in expulsion, every act of that kind being 

 preceded or accompanied 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, 

 laughing 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 perineal region in the male, 

 are the 



Accelerator urinae, Sphincter ani, 



Erector penis, Levator ani, 



Compressor urethra, Coccygeus. 

 Transversus perinei, 



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 which demands some degjee 

 of delicacy and nice manipulation, a strong light should be thrown upon 

 the part. Having fixed the subject, and drawn the scrotum upwards by 

 means of a string or hook, carry an incision from the base of the scrotum 

 along the ramus of the pubes and ischium and tuberosity of the ischium, 

 to a point parallel with the apex of the coccyx ; then describe a curve 

 over the coccyx to the same point on the opposite side, and continue the 

 incision onwards along the opposite tuberosity, and along the ramus of the 

 ischium and of the pubes, to the opposite side of the scrotum, where the 

 two extremities maybe connected by a transverse incision. This incision 

 will completely surround the perineum, following very nearly the outline 

 of its boundaries. Now let the student dissect off the integument care- 

 fully from the whole of the included space, and he will expose the fattj 

 cellular structure of the common superficial fascia, which exactly resembles 

 the superficial fascia in every other situation. The common superficial 



