362 MUSCLES AXD FASCIAE. 



crest of the ilium, and from the lumbar fascia. From this origin, the fibres 

 diverge ; those from Poupart's ligament, few in number and paler in color than 

 the rest, arch downwards and inwards across the spermatic cord, to be inserted, 

 conjointly with those of the Transversalis, into the crest of the os pubis and 

 pectineal line, to the extent of half an inch, forming what is known as the 

 conjoined tendon of the Internal Oblique and Transversalis ; those from the 

 anterior superior iliac spine are horizontal in their direction ; whilst those 

 which arise from the fore part of the crest of the ilium pass obliquely upwards 

 and inwards, and terminate in an aponeurosis, which is continued forwards to 

 the linea alba; the most posterior fibres ascend almost vertically upwards, to 

 be inserted into the lower borders of the cartilages of the four lower ribs, 

 being continuous with the Internal Intercostal muscles. 



The conjoined tendon of the Internal Oblique and Transversalis is inserted 

 into the crest of the os pubis and pectineal line, immediately behind the exter- 

 nal abdominal ring, serving to protect what would otherwise be a weak point 

 in the abdomen. Sometimes this tendon is insufficient to resist the pressure 

 from within, and is carried forward in front of the protrusion through the ex- 

 ternal ring, forming one of the coverings of direct inguinal hernia. 



The aponeurosis of the Internal Oblique is continued forward to the middle 

 line of the abdomen, where it joins with the aponeurosis of the opposite mus- 

 cle at the linea alba, and extends from the margin of the thorax to the pubes. 

 At the outer margin of the Rectus muscles, this aponeurosis, for the upper 

 three-fourths of its extent, divides into two lamella, which pass, one in front 

 and the other behind the muscle, inclosing it in a kind of sheath, and reuniting 

 on its inner border at the linea alba; the anterior layer is blended with the 

 aponeurosis of the External Oblique muscle; the posterior layer with that of 

 the Transversalis. Along the lower fourth, the aponeurosis passes altogether 

 in front of the Rectus without any separation. 



Relations. By its external surface, with the External Oblique, Latissimus 

 Dorsi, spermatic cord, arid external ring. By its internal surface, with the 

 Transversalis muscle, fascia transversalis, internal ring and spermatic cord. Its 

 lower border forms the upper boundary of the spermatic canal. 



Dissection. Detach the Internal Oblique in order to expose the Transversalis beneath. This 

 may be effected by dividing the muscle, above, at its attachment to the ribs ; below, at its con- 

 nection with Poupart's ligament and the crest of the ilium ; and behind, by a vertical incision 

 extending from the last rib to the crest of the ilium. The muscle should previously be made 

 tense by drawing upon it with the fingers of the left hand, and if its division is carefully effected. 

 the cellular interval between it and the Transversalis, as well as the direction of the fibres of 

 the latter muscle, will afford a clear guide to their separation ; along the crest of the ilium the 

 circumflex iliac vessels are interposed between them, and form an important guide in separating 

 them. The muscle should then be thrown forwards towards the linea alba. 



The Transversalis (Fig. 232), so called from the direction of its fibres, is the 

 most internal flat muscle of the abdomen, being placed immediately beneath 

 the Internal Oblique. It arises by fleshy fibres from the outer third of Pou- 

 part's ligament, from the inner lip of the crest of the ilium, its anterior three- 

 fourths, from the inner surface of the cartilages of the six lower ribs, inter- 

 digitating with the Diaphragm, and by a broad aponeurosis from the spinous 

 and transverse processes of the lumbar vertebne. The lower fibres curve 

 downwards, and are inserted, together with those of the Internal Oblique, into 

 the crest of the os pubis and pectineal line, forming what was described above 

 as the conjoined tendon of these muscles. Throughout the rest of its extent 

 the fibres pass horizontally inwards, and near the outer margin of the Rectus, 

 terminate in an aponeurosis, which is inserted into the linea alba ; its upper 

 three-fourths passing behind the Rectus muscle, blending with the posterior 

 lamella of the Internal Oblique; its lower fourth passing in front of the Rectus. 



Relations. By its external surface, with the Internal Oblique, the inner sur- 

 face of the lower ribs, and Internal Intercostal muscles. Its inner surface is 



