Vijayamma Kunnath Narayanan1, Serin Peter2, Anjana Jayakumaran Nair3

The rectus abdominis is a long, flat strap muscle which extends vertically upward along the linea alba from the pubic symphysis below to the costal margin above. It is a flexor of the vertebral column and thereby plays an important role in maintaining the normal body posture. As it is a part of the anterior abdominal wall, the strength of the muscle plays a very important role in maintaining the integrity of the anterior abdominal wall. Weakness of the rectus abdominis is seen mainly in multiparous women resulting in the divarication of the recti. The lateral border of the rectus abdominis forms the medial boundary of the Hesselbach’s triangle, which is the commonest site of direct inguinal hernia. It arises by two tendinous heads: Medial head arises from the anterior surface of the pubic symphysis and the lateral head arises from the lateral part of the pubic crest and the pubic tubercle. The muscle is inserted on the anterior thoracic wall by four fleshy slips along a horizontal line passing laterally from the xiphoid process and cutting in that order, the 7th, 6th and 5th costal cartilages. The paired recti muscles are separated in the median plane by the linea alba. The muscle is three times as wide superiorly as inferiorly. It is broad and thin superiorly and narrow and thick inferiorly. It has a tendinous origin and a muscular insertion that is in the form of four fleshy slips that are attached in a horizontal manner to the lower part of the anterior thoracic wall. The rectus abdominis is enclosed in the rectus sheath, which is formed by the aponeuroses of the anterolateral muscles of the anterior abdominal wall. The muscle usually presents tendinous intersections along its length.
The study was carried out in the Department of Anatomy, Government Medical College, Kottayam by the dissection of 20 adult cadavers and 5 foetal cadavers during the routine dissection time of the undergraduates and postgraduates. The cadavers were obtained after ethical clearance and were embalmed prior to the study. The rectus sheath was cut by a midline incision to expose the muscle. Measurements were taken, intersections noted and photographed.
Majority of the cadavers studied (88%) had four tendinous intersections that were adherent to the anterior wall of the rectus sheath, but loosely attached to its posterior wall. This was against the description of three intersections seen in most of the anatomy books. The tendinous intersections above the level of umbilicus were complete in all the cadavers studied. There was also a marginal left-sided preponderance in the length of the rectus abdominis in both male and female cadavers. The pyramidalis muscle was seen to be absent in 25% of the cadavers. None of the foetal cadavers showed tendinous intersections.
The tendinous intersections help to increase the power of the muscle by dividing it into columns partially or completely. The presence of four tendinous intersections in most of the cadavers studied was a surprising finding. The absence of tendinous intersections in the foetal specimens could imply that they fully develop after birth, probably after the child becomes ambulant.