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



The name supracostal given to this muscle by Dr. Murie is confusing, for thus we should 

 understand that the muscle is the musculus rectus thoracis of Professor Sir Wm. Turner, and the 

 supracostal of Mr. Wood and others. 1 In Phoca the rectus tendon is unbroken and reaches the 

 cartilage of the 1st rib beneath the sterno-costalis ; in Arctocephalus the rectus ends posterior to the 

 origin of this muscle, but the fibres of the sterno-costalis anterior, as in Phoca, are obliquely directed 

 outwards and not antero-posteriorly. In Murie 's dissections it does not touch the sternum, but the 

 situation and direction of the fibres in his plates are the same as in Phoca and Arctocephalus ; so 

 I do not regard Murie's supracostal as a part of the rectus which the name he uses indicates. 



The Sterno-costalis posterior is the transversus tenuis of Lucae. It is only found in Phoca vitu- 

 lina, and arises from the mesosternum at its junction with the cartilages between the 3rd and 7th 

 ribs, and from the tendon of the rectus which passes forwards beneath it. On the right side it 

 receives a muscular slip from the xiphisternum and then divides into three slips, which are inserted 

 into the outer surfaces of the 1st, 2nd, and 3rd ribs. The first digitation is fixed outside the origin 

 of the sterno-thyro-hyoid ; the second and third beside the origins of the serratus, these two being 

 crossed by the origin of the scalenus posticus. This part may not be quite separate from the 

 anterior. 



The External intercostals in Phoca vitulina commence close to the side of the vertebral column, 

 and leave only a hollow for the levatores. They arise from the posterior part of the rib joints 

 by a few fibres, at the outer side of the levatores they thicken, and then pass from the ribs in 

 front backwards and outwards to the ribs behind. They extend from end to end of each rib. 



In Arctocephalus they extend from the heads of the ribs to the middle of the costal cartilages. 



The Internal intercostals in Phoca vitulina are quite close to the vertebra?, where the subcostals 

 are wanting. They arise from the anterior part of the rib joints, and from the anterior borders of the 

 ribs, and are inserted into the posterior borders of the ribs sternad to their origins, the fibres of 

 the muscles almost meeting over the ribs. There is an aponeurosis between the two muscles, 

 strongest near the column and almost disappearing about the middle of the bony ribs. In the last 

 space the muscle lies only on the outer half of the rib, and begins at the outer edge of the scalenus 

 lumborum. 



In Arctocephalus they arise from the whole anterior borders of the ribs to their necks, and from 

 the same borders of the cartilages. The fibres are inserted into the posterior borders of the ribs 

 sternad to their origins, and end at the sternebrae. 



The Scalenus lumborum is so named by G. H. Meyer in the human body. 2 In Phoca vihdina 

 it arises from the transverse processes of all the lumbar vertebrae by an aponeurosis, and forms a 

 triangular muscle with the apex posterior. It is inserted in its outer half into the posterior 

 border of the outer half of the last rib ; the inner half crosses over this rib and is strengthened 

 by a few fibres from it ; whilst the outer half of this portion goes into the 14th rib, the inner crosses 

 over to the 13th rib, and ends on its posterior border. 



In Arctocephalus it arises from the transverse processes of the 1st, 2nd, and 3rd lumbar verte- 

 brae, forming a thin triangular sheet with the base forwards. It is inserted into the last three ribs. 

 A portion of its fibres from the outer side is attached to each of the last two ribs, the remainder to 

 the 13th rib, but the proportion in which the fibres are distributed differs from that in Phoca — 



1 Sir Wm. Turner, Proc. Roy. Soc. Edin., vol. vi. pp. 268, 270, 1869. 

 - Lehrbuch der Anatomie, 1855. 



