424 THE MUSCULATURE 



ligamentum teres in the female. The eremaster muscle is attached laterally 

 to the inguinal ligament, medialty to the outer layer of the sheath of the rectus 

 near the insertion of the latter. 



The inner layer of the thoraco-abdominal musculature is composed of fibre 

 bundles which take a course transversely across the body. In the thoracic region 

 it is represented by the transversus thoracis (fig. 386), a slightly developed muscle 

 which arises from the costal cartilages of the third to sixth ribs and is inserted into 

 the lower part of the sternum and into the xiphoid process. In the upper portion 

 of the muscle the fibre-bundles extend obliquely downward and forward instead of 

 transversely. In the abdomen this laj^er is represented by the transversus 

 abdominis (fig. 390) which arises from the cartilages of the lower seven ribs, from 

 the lumbo-dorsal fascia, the iliac crest and lateral part of the inguinal ligament and 

 is inserted into the linea alba by means of an aponeurosis which lies behind the 

 rectus in the upper two-thirds of the ventral wall of the abdomen and in front in 

 the lower third. It is intimately fused with the aponeurosis of the internal 

 oblique. 



The main trunks of the anterior divisions of the last five or six thoracic nerves 

 give rise to branches which suppty the muscles both of the middle and inner layers 

 of the lateral thoraco-abdominal musculature. In the abdominal region these 

 trunks run in the main between the two layers. Some muscular branches are 

 usually also supplied from the ilio-hypogastric and ilio-inguinal nerves. In the 

 thoracic region the intercostal nerves run external to the subcostal muscles, 

 through the substance of the costal part of the internal intercostal muscles, and 

 internal to the parts of the internal intercostals which lie between the costal 

 cartilages. Eisler includes the subcostal muscles and that part of the internal 

 intercostals which lies internal to the nerve trunk, with the inner rather than with 

 the middle layer of the thoracic musculature. 



The ventral part of the muscular thoraco-abdominal wall is represented by a 

 single muscle on each side, the rectus abdominis muscle, except just above the 

 symphysis pubis where the rudimentary pyramidalis is usually found. The rec- 

 tus abdominis muscle (fig. 388), is a band-like muscle which arises from the ventral 

 surfaces of the fifth to the seventh costal cartilages and from the xiphoid process 

 and is inserted into the superior ramus of the pubis. It is ensheathed by the ap- 

 oneuroses of the lateral abdominal musculature described above. The component 

 fibre-bundles run nearly parallel with the mid-sagittal line. Transverse inscrip- 

 tions partially divide the muscles into segments. It is innervated by the last six 

 or seven thoracic nerves. The pyramidalis (fig. 388) is a small muscle which 

 arises from the superior pubic ramus and is inserted into the linea alba for about a 

 third of the distance to the umbilicus. 



The lateral intertransverse muscles of the lumbar region described on p. 417 

 probably belong to the ventro-Iateral musculature of the trunk. The nerves 

 supplying them come from the junction between the posterior and anterior 

 divisions of the spinal nerves. 



The inguinal (Poupart's) ligament and the inguinal canal, described in detail 

 below, are of considerable practical interest because of the frequency of hernias 

 in this region. In the quadrupeds the pressure of the weight of the abdominal 

 viscera centres toward the umbilicus while in man it centres toward the ventral 

 part of the line of attachment of the abdominal wall to the pelvis. The lower 

 margin of the aponeurosis of the external oblique muscle is here strengthened to 

 form the inguinal (Poupart's) ligament which extends from the anterior superior 

 iliac spine to the pubic tubercle. Near the latter it is reflected (curves medial- 

 ward) to the j)ubic crest forming the triangular lacunar ligament (Gimbernart's). 

 The medial half of the inguinal ligament helps to bound a slit-like space, inguinal 

 canal through whicli in the male the spermatic cord passes to the scrotum, and in 

 the female, the round ligament passes to the labium majus. This canal begins on 

 the inner side at the (internal) abdominal ring, which is situated above and medial 

 to the centre of the inguinal ligament. The canal, which is about 4 cm. long, 

 extends rncdialward and downward to the subcutaneous (external abdominal) 

 ring, a slit-like oi)ening in the aponeurosis of the external obli(iU(^ just above the 

 inguinal ligament. The canal is bounded ventrally by the aponeurosis of the ex- 



