234 THE VOYAGE OF H.M.S. CHALLENGER. 



the dorsal sacro-iliac ligament, and from the transverse processes of all the sacral vertebrae, and is 

 inserted into the transverse processes of all the caudal vertebra, partly by tendon and partly by 

 muscular fibres. 



Some of the Perineal Muscles. 



The Sphincter ani in the female Phocinse and the female Arctocephcdus is a broad, strong band. 

 It arises from the ventral mesial caudal region, and encircles the posterior end of the rectum and 

 vagina, but in the male it only winds round the rectum. 



The Levator ani in Plwca vitidina is a triangular muscle. It arises from the anterior inner 

 wall of the pubes, ending half an inch anterior to the posterior margin of the obturator foramen ; 

 from one inch of the pubic bar at the anterior margin of the obturator foramen ; between these two 

 points of origin from the obturator fascia close to the ventral margin of the obturator foramen : 

 from the internal surface of the innominate bone dorsal to the obturator nerve, and posterior to the 

 sacro-iliac articidation ; and from the lateral and ventral surfaces of the 2nd, 3rd, and 4th sacral, and 

 1st and 2nd caudal vertebra?. It forms several tendons and these proceed backwards ; the inner- 

 most is inserted into the ventral mesial surface of the 5th caudal vertebra, the outermost into the 

 ventral surface of the transverse process of the same vertebra, and the other three tendons into the 

 ventral surfaces of the last caudal vertebra by passing backwards between the other two insertions. 

 From the middle of the 2nd caudal vertebra to the back of the 4th sacral, many fibres pass 

 down around the rectum and vagina, and proceed backwards beneath the sphincter for the vagina 

 and rectum. The combined levators form a funnel-shaped tube which passes through the pelvic 

 outlet surrounding the rectum and vagina. 



In Arctocephalus it arises from the inner surface of the pubic bar above the pelvic brim, between 

 the pectineal eminence anteriorly and the side of the symphysis posteriorly; from the inner surface 

 of the ilium anterior to the obturator foramen ; and from the ventral sides of the sacral and caudal 

 vertebrae. The levators form a muscular tube as in Phoca, the posterior pubic fibres proceed back- 

 wards and encircle the vagina and rectum, but principally the former. Then they turn inwards 

 upon the ventral side of the vagina, and end posteriorly among the fibres of the sphincter for the 

 vagina and rectum outside the pelvis. The rest of the fibres run backwards along the caudal 

 region, and are inserted into the ventral surfaces of the transverse processes of the caudal vertebrae. 



The Protractor of the prepuce, hi the Phoeinre between the symphysis pubes and the umbilicus, is 

 a muscular band arising from the outer border of the rectus by three slips. These soon unite, 

 proceed backwards, and are inserted into the side of the prepuce around the orifice, the fibres of 

 both muscles meeting on its ventral surface. 



The Retractor vagina? in Phoca is a quadrilateral muscle. It arises half an inch ventral to the 

 ischial spine from the posterior borders of the ischium and pubes, and descends upon the side of the 

 vagina, being dorsally blended with the levator ani. 



