150 EQUINE ANATOMY. 



THE PERINEUM. 



The perineum is the space lying below the rectum, and on the 

 sides of the external genitals in both sexes. 



Superficial fascia. 



Arises from the inner sides of thighs. Inserted on muscles of 

 perineum and sphincter ani. 



Deep fascia. 



Arises from ischial tuberosities, rectal muscles and thighs. 



Inserted, between ischio-cavernosus and semi-membranosus, 

 into perineal muscles and fascia. 



Muscles. 



(a) Wilson's muscle. 

 Origin. From sides of pelvis. 



Insertion. By superior and inferior fasciculi into urethra in its 

 membranous portion. 



(b) Accelerator urince. 



Origin. From under surface of the urethra. 

 Inserted. Into top of urethra often passing around it; extend- 

 ing from ischium to end of penis by transverse fibres. 



(c) Ischio-urethral (compressor urethrse). 

 Origin. From ischial arch. 



Insertion. Into lower face of Cowper's gland and Wilson's 

 muscle. 



(d} Transversus perinei. ' 



Origin. Ischial spine. 



Insertion. Into median perineal line. 



Action of Muscles. 



The first and third compress the urethra. 



The second acts more especially in emptying it of urine, or 

 semen. 



The fourth dilates the urethra. 



FEMALE GENITALS. 



THE VULVA. 



The external orifice of the female genitals is situated below the 

 anus in the perineum. It is a slit-like opening, extending verti- 

 cally, terminated above and below in the superior and inferior 

 commissures. The sides are formed by the labice (or lips), of 



