MAY, 1921. AMERICAN MARSUPIAL, C^ENOLESTES OSGOOD. 35 



terior border of the scapula where it is continuous with the levator 

 scapulae. 



Scalenus. This has two fairly distinct divisions, at least posteriorly. 

 The scalenus medius, or larger division, takes origin from the superior 

 transverse processes of the third, fourth, and fifth cervical vertebrae 

 over which it is somewhat narrow and thickened. Thence passing caudad 

 it becomes thin and flattened and inserts by broad distinct slips on the 

 middle of the third and fourth ribs, one slip on the third and two on the 

 fourth, passing beneath and separating digitations of the serratus 

 magnus in so doing. The scalenus anticus has its origin in coalescence 

 with the medius, but about midway between the third cervical vertebra 

 and the first rib it separates and inserts on the front of the first rib 

 directly opposite the insertion of the supracostalis. 



MUSCLES OF THE ABDOMEN. 



Rectus abdominis. Origin from the pubis and marsupial bone. In- 

 sertion on the sternal part of the first rib and on the adjoining side of the 

 manubrium of the sternum. It is strong and well developed anteriorly, 

 broader but thinner abdominally. 



Obliquus externus abdominis. Origin from the middle of the sides of 

 the ribs from the fourth to the twelfth, interdigitating anteriorly with 

 the serratus. Thence it follows the lumbar fascia to Poupart's ligament 

 which is inserted at the inner anterior base of the marsupial bone. 

 Ventrally it spreads over the abdomen covering the rectus and inserting 

 by aponeurosis on the linea alba. 



Obliquus internus abdominis. Origin from Poupart's ligament and 

 the ilium and thence dorsad to the lumbar fascia and craniad to the 

 posterior borders of the loth to i3th ribs. It is fleshy in its dorsal portion 

 down to a line from the ventral third of the costal cartilage of the tenth 

 rib diagonally across the side of the abdomen to the pubic region. Ven- 

 trad of this line the transversalis appears and no aponeurosis of the 

 obliquus is demonstrable in the material available. 



Transversus abdominis. Origin from the inner sides of the nth, 

 1 2th, and i3th ribs and from a coalescence with the diaphragm and 

 thence along the lumbar fascia to the ilium. Ventrally it is inserted 

 into the linea alba. Posteriorly it is broadly aponeurotic and anteriorly 

 mostly fleshy. 



Cremaster. Arises in the male beneath the internal oblique near the 

 crest of the ilium, and passes ventro-caudad across the iliacus and psoas 

 major in the plane of the transversalis but separated from it by a slight 

 space. It passes out of the body cavity through the ring in front of the 



