REPORT ON THE SEALS. 219 



differs from the above : on the right side it arises from the anterior and outer surface of the 1st rib, 

 extending from its junction with the cartilage nearly to the inner third of the rib. It runs 

 forwards and is inserted into the root of the outer side of the ventral division of the transverse 

 process of the 6th cervical vertebra by muscular fibres, into the posterior end of the ventral 

 division of the 5th cervical vertebra by a tendinous slip, and likewise into the corresponding part 

 of the 3rd and 4th cervical vertebra. It is supplied by the brachial plexus. 



The Scalenus 2)ostic2is in Phoca vitulina is much the largest of this group, and arises from the 

 posterior border of the 4th rib at the junction of the cartilage with the rib ; and similarly from 

 the posterior border and outer surface of the 3rd rib. The digitation of the serratus coming from 

 the 3rd rib lies between these two points of origin. It is inserted into the ventral hatchet-shaped 

 division of the transverse processes of the 3rd and 4th cervical vertebrae by two strong tendons. 

 In the large Phoca vitulina the origin is similar, but the insertion is by tendons into the posterior 

 of the ventral divisions of the transverse processes of the 3rd and 4th cervical vertebras, these 

 tendons being common to the scalenus secundus. It is supplied by the brachial plexus. 



In ArctocepJuilus it lies in the cervical region and is of the same shape as the anticus, but 

 smaller. It arises from the ventral tip of the transverse process of the 7th cervical vertebra, and 

 is inserted into the ventral border of the transverse process of the atlas, dorsal to the anterior 

 oblique portion of the longus colli, into the dorsal tip of the transverse process of the 3rd cervical, 

 and into the dorsal divisions of the same processes of the 4th, 5th, and 6th cervical vertebrae. 



The Muscles of the Thorax. 



In Phoca vitulina we find the sterno-costalis anterior and posterior, internal intercostals, external 

 intercostals, scalenus lumborum, levatores costarum, and triangularis sterni. In Arctoceplialus the 

 sterno-costalis posterior is wanting, otherwise the muscles are alike. 



The Sterno-costalis anterim' is Lucae's transversus costarum latus and Murie's supracostal. In 

 Phoca vitulina it lies next the sternum, and is a flat slender layer of muscle which arises from the 

 side of the presternum and mesosternum as far back as the 6th rib, and from the cartilages of the 

 1st to the 6th ribs at their junction with the sternum. It remains tendinous to 1 inch from the 

 side of the sternum, then it becomes muscular, and ultimately divides into three digitations, the 1st 

 being the longest. It is inserted into the outer surface and cartilage of the 1st rib, extending 

 outwards to the digitation of the serratus, into the posterior border of the 2nd rib close to the 

 digitation of the serratus, and into the same part of the 3rd rib. 



In Arctoccphalus it is a small triangular muscle, and arises from the sides of the 2nd, 3rd, and 4th 

 sternebrae, from the cartilages of the 2nd, 3rd, 4th, and 5th ribs by a fine aponeurosis. The fibres 

 run forwards and outwards, and are inserted into the posterior border of the cartilage of the 1st rib, 

 and into the 2nd at the junction of the cartilage with the rib. 



Lucae figures it attached to the sternum and the ribs, covering the tendon of the rectus (pi. 

 vi. fig. 1), but describes it as going from the 4th rib to the 1st cartilage and rib, with its tendon 

 united to that of the rectus. 



In Otaria it lies to the sternal side of the scalenus anticus between the cartilages of the 3rd 

 and the 1st ribs. 



In Trichechus it extends from the 4th costal cartilage to the 2nd rib and 1st intercostal space. 



