MALE GENITAL SYSTEM: MUSCULATURE 3 6 9 



least important of these is the insertion upon the ectal border of the rudimentary pelvis 

 (iliac portion, Fig. i / 2 ). Of the two main terminations the superficial one is a triangular 

 wedge of muscle which thins out upon the fibrous fascia between the hypaxial muscle 

 and the origin of the ischio-caudalis. It thus forms a lateral wedge bounding the 

 external genital structures (Fig. i / 3 ). The third and main insertion of the rectus upon 

 the chevron bones can only be seen when the main body of the rectus and the rudi- 

 mentary pelvis are drawn aside (Fig. i I 1 ). The fibres of this deep portion of the muscle 

 run dorsally and caudally to be inserted upon the anterior chevron bones. The insertion 

 of the rectus caudally is thus threefold. Between the deep and superficial parts of this 

 insertion (that is between the portion inserted upon the chevron bones and the iliac 

 portion) a foramen is left through which nerves and blood vessels obtain admission to 

 the penis (and to the clitoris in the female). 



The transversalis muscle has already been mentioned. It is a thin transverse sheet 

 passing dorsal to the rectus muscle between the latero-dorsal aponeuroses of opposite 

 sides of the body. Its extent is about the same as that of the obliquus internus. 



The ischio-caudalis (Fig. i / 5 ) is a broad but thin sheet on each side of the mid-ventral 

 line in the caudal region. Dorsally it is bounded by the deep portion of the hypaxial 

 muscle and laterally by the superficial part. In the middle line the antimeres of the two 

 sides are separated by a thin raphe as far forward as the anus, where they diverge to give 

 passage to the rectum (Fig. i o). Anteriorly the ischio-caudalis muscles of each side 

 arise extensively by their lateral fasciculi from the inner sheath of the rectus abdominis 

 and by their inner fasciculi from the ectal margin of the ischial portion of the pelvis. 

 The fibres of the ischio-caudalis extend inwards and caudally and are inserted (Schulte) 

 upon the tips of the chevron bones as far back as the junction of the pedicle with the 

 flukes. Between the ischio-caudalis and the hypaxial muscle, opposite the tip of the 

 triangular insertion of the rectus, a large lumbar vein from the surface of the pedicular 

 region is admitted, running forwards and inwards to its junction with the iliac vein 

 (Fig. i & 3 ). No artery accompanies this vein, but there is a stout lumbar nerve running 

 with it from the main genital nerve from which it arises in the inguinal region. 



Anteriorly the ischio-caudalis of each side diverges from its antimere to give passage 

 to the anus and rectum. From the anus forward to the penis the ischio-caudalis muscles 

 are separated by a transverse sheet of muscle — the levator ani (Fig. i / 4 ). This muscle 

 is fairly thin in the male but considerably thicker in the female. It takes origin from the 

 deep surface and inner border of the ischio-caudalis and its fibres are continued on to 

 the base of the bulbus penis of the male and the walls of the vulva of the female 

 (Fig. 1 1 /). The antimeres of opposite sides are united in the mid-ventral line below the 

 rectum by a raphe. Schulte describes the levator ani as taking origin anteriorly from 

 the ental surface of the pelvis, but this was not confirmed. 



A small transverse muscle, the coccygeus, was found behind the anus (Fig. i Z 11 ). 



The hypaxial muscle (Fig. i /«) is an immense mass extending throughout the whole 

 length of the body ventral to the transverse processes of the vertebral column and 

 occupying, in the lumbar and pedicular regions, the space between the transverse 



