222 THE VOYAGE OF H.M.S. CHALLENGER. 



sides of the 3rd, 4th, 5th, and 6th sternebrae by a narrow tendon. The fibres pass transversely 

 outwards posteriorly, and slightly outwards and forwards anteriorly, and terminate laterally 1 inch 

 to the outer side of the sternum. It is inserted into the cartilages of the 3rd to the 8th ribs, and 

 into the fascia between them upon the intercostal muscles. These muscles are supplied by the 

 intercostal or lumbar nerves. 



The Muscles of the Abdomen. 



In Phoca vitulina and in Arctoccphalus these are the external oblique, internal oblique, trans- 

 versalis, rectus abdominis, and cremaster. The pyramidalis and quadratus lumborum are wanting. 



The Obliquus externus abdominis in Phoca vitidina is much the strongest of the abdominal group. 

 It has fourteen digitations. The first arises from the outer and posterior surface of the 4th rib, inter- 

 digitating with the serratus magnus, and, after mingling with a few of the fibres of the first or 

 anterior head of the scalenus posticus, is partially crossed by part of the same muscle from the 5th 

 rib. The second digitation from the outer and posterior surface of the 5th rib interdigitates with the 

 serratus and touches the origin of the posterior slij) of the scalenus posticus, which passes beneath 

 the digitation of the serratus from this rib. The third to the seventh spring from the outer and 

 posterior surfaces of the 6th to the 10th ribs, interdigitating with the serratus magnus only. The 

 eighth to the thirteenth digitations spring from the outer and posterior surfaces of the 10th to the 

 15th ribs, interdigitating with the latissimus dorsi. The digitation from the last rib is the largest of 

 the series from ribs. The fourteenth digitation has no bony origin, but comes from the lumbar fascia, 

 interdigitating with the latissimus dorsi, and is still larger than the thirteenth. The fibres from the 

 first and second digitations run backwards and inwards and terminate near the inner edge of the 

 rectus muscle, and are continuous with the fascia covering its posterior surface ; those from the 

 third and fourth have the same course, but form an aponeurosis near the inner edge of the rectus, and 

 join the aponeurosis of the other side. From behind the ensiform cartilage to the symphysis pubis 

 the muscle terminates in an aponeurosis upon the outer border of the rectus, the fibres of one side 

 decussating with those of the other. The anterior digitations run obliquely backwards and inwards, 

 the middle more so, and those fibres coming from the posterior ribs and the dorsal fascia are nearly 

 antero-posteriorly directed. The muscle is thinnest at its anterior end and thickest at its posterior 

 and dorsal side, and does not thin off at the side of the rectus but ends abruptly as a tendon. The 

 dorsal border behind the last digitation overlies the lumbar fascia, and is kept in its position by the 

 fascia over the surface of the muscle passing on to it. The dorsal edge of the muscle runs directly 

 backwards to a little to the outer side of the patella, whence the posterior border runs obliquely 

 backwards and inwards to the symphysis in a direct line from the patella. From the posterior 

 border, midway between the outer edge of the patella and the symphysis, two strong flat tendons 

 are developed ; the outermost goes behind the cord and is attached to the brim of the pelvis a 

 little more than 1 inch to the anterior side of the symphysis, its posterior border being posterior 

 at the attachment. From the anterior border of this a thin triangular aponeurosis is attached 

 to the brim of the pelvis, extending from the anterior part of the outer pillar to an inch and a 

 quarter posterior to the pectineal eminence. 



In ArctoccpJialus it arises by ten digitations from the posterior and outer surfaces of the 6th to 

 the 15th ribs, each digitation ending about half an inch from the junction of the ribs with their 



