454 LABORATORY MANUAL OF HUMAN ANATOMY 



ward, noting its digitations and the muscles to which it is related. 

 (Cf. Spalteholz, Fig. 317.) Examine the course of the N. ilio- 

 inguinalis. 



(b) Internal oblique muscle of abdomen (M. obliquus internus ab- 



dominis). 



What is meant by the inguinal aponeurotic falx (falx aponeu- 

 rotica inguinalis) (0. T. conjoined tendon)? 



O-n the right side only, divide this muscle where the fibres 

 pass over into the aponeurosis and also along a line five milli- 

 metres above the inguinal ligament and crista iliaca. Reflect 

 the muscle dorsalward and cranialward, noting carefully the 

 vessels and nerves on its deep surface. What are they? (Cf. 

 Spalteholz, Figs. 319 and 324.) Note where the lateral cuta- 

 neous rami of the intercostal nerves perforate this muscle. 

 What is the relation of the M. cremaster to the M. obliquus in- 

 ternus abdominis? 



(c) Transverse muscle of abdomen (M. transversus abdominis). 



Note carefully the relation of the falx inguinalis to the annulus 

 inguinalis subcutaneus. Note where the fibres go over into the 

 aponeurosis, the semilunar line (linea semilunaris [Spigeli]). 



On each side make an incision through the aponeuroses paral- 

 lel to the linea alba and distant three centimetres from it, extend- 

 ing throughout the entire length of the M. rectus abdominis. 

 Eeflect the flaps of the aponeuroses lateralward and medialward 

 respectively. Difficulty in reflecting is experienced along the 

 transverse line, owing to attachment to the subjacent muscle. 

 These transverse lines are the inscriptiones tendineae. How 

 many of them are there? Where are they situated? What is 

 their morphological significance? 



(d) Rectus ("straight") muscle of abdomen (M. rectus abdominis). 



Study its sheath (vagina recti abdominis). Note the disposition 

 in its upper two-thirds and in the lower third. What theories have 

 been advanced to explain this arrangement? How is the semi- 

 circular line of Douglas ( linea semicircularis [Douglasi] ) formed ? 



Note the vessels and nerves which pass through the posterior 

 layer of the sheath; also the artery passing from below upward 

 (A. epigastrica inferior) and the one passing from above down- 

 ward (A. epigastrica superior). Do these anastomose in the 

 muscle ? 



(e) Pyramidal muscle (M. pyramidalis) . 



What is its relation to the M. rectus abdominis and its sheath? 

 What is the phylogenetic significance of this muscle? 



This muscle is frequently absent, and also varies greatly in 

 length, sometimes extending as high as the umbilicus. 



