196 MUSCLES OF THE PERINEUM. 



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 flex- 

 ing the vertebral column forwards. The diaphragm is an inspira- 

 tory 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 ensiform cartilage, to that of the upper 

 lumbar vertebra. During relaxation it is convex, and encroaches 

 considerably on the cavity of the chest, particularly at the sides, 

 where it corresponds with the lungs. It assists the abdominal mus- 

 cles powerfully in expulsion, every act of that kind being preceded or 

 accompanied by a deep inspiration. Spasmodic action of the dia- 

 phragm 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 pel- 

 vis, 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 this region in the male, are the 



Accelerator urince, 

 Erector penis, 

 Transversus perinei, 

 Compressor urethras, 

 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 which demands some degree of delicacy and nice manipu- 

 lation, 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 pubis 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 pubis, to the opposite side of the 

 scrotum, where the two extremities may be connected by a trans- 

 verse incision. This incision will completely surround the perineum, 

 following very nearly the outline of its boundaries. Now let the stu- 



