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



anguli scapulae in Otaria and Trichechus resembling in insertion the muscle of human anatomy. In 

 all the Phocinre and the two Arctoccphali I find there is one with a very similar insertion to that 

 found in man, so there is reason for giving the name atlanto-scapular to the muscle in Arctoccphalu* 

 corresponding to Dr. Murie's levator anguli scapula?. 



In his paper on the Trichechus he points out that there is also a muscle which may be the 

 representative of the so-called levator-claviculfe. The atlanto-humeral has the same action as the 

 cephalo-humeral. The atlanto-scapular pulls the scapula forwards and rotates it. 



Up to the present there have been differences in the muscles of Phoca barhata and Phoca 

 hispida, and special descriptions of various points have been required ; but now we come to a stage 

 in this myological study where all these agree, with only an occasional difference. It must there- 

 fore be remembered that the description of Phoca vitulina is also the description of Phoca barhata 

 and Phoca hispida, and only when a deviation occurs from the one selected as the standard animal 

 will their names be cited. 



The Ventral Thoracic Eegion contains the pectoral muscle. The pectoralis minor and sub- 

 clavius are absent. 



TJic Pectoral Muscle. — In consequence of the importance of this muscle both in swimming 

 and in moving on land, I have very carefully examined it. It has received numerous names. 

 Vrolik and Humphry call it the pectoralis major, Lucae the pectoralis, and Murie in the Otaria the 

 pectoral muscles, whilst in the Trichechus he divides it into three — (a) a fleshy pectoralis major, (b) a 

 second, (c) a third layer. It is situated in the pectoral region at its insertion, but the origin is more 

 extensive, for it covers the neck, chest, abdomen, and leg. The panniculus partially conceals it. 

 This most extensive muscle is divisible into three parts — (a) the presternal, (b) the sternal, and (c) 

 the abdominal. The presternal and sternal form one triangle, the abdominal another. The 

 presternal part arises from the fascia over the trachea 1 inch anterior to the presternum, and from 

 the side of it. It is separated, close to the junction of the presternum with the meso-sternum, by a 

 very faint cellular line, seen best on the under surface of the muscle. The fibres pass towards the 

 shoulder. The sternal part arises from the whole length of one side of the meso-sternum, and from 

 the cartilages of the eleven true ribs, and by an antero-posterior slip from the xiphi-sternum. A 

 cellular interval separates it from the third part. The abdominal part must be studied as three groups 

 of fibres. The first group arises posterior to the xiphi-sternum from 3£ inches of the linea alba ; the 

 second group, from the fascia over the external oblique muscle, by several finger-like prolongations, 

 which are shortest and most obliquely directed outwards near the middle line. Between these the 

 fibres of the external oblique are seen ascending to the ribs. The third group arises from the fascia 

 on the back of the leg. These hindmost fibres rest on the back of the leg, are continuous with the 

 hindmost fibres of the panniculus, turn round the leg, sweep over the femur, touch the outer side of 

 the patella, and course antero-posteriorly with the rest of the abdominal fasciculi, which are obliquely 

 turned outwards. All meet at the axillary border of the sternal part and disappear beneath it. 

 The three parts — presternal, sternal, and abdominal — converge on nearing their attachment to the 

 humerus. They are inserted in the following manner : — The presternal part blends with the sternal, 

 and the anterior third of this combination is inserted into the inner margin of the deltoid tuberosity of 

 the humerus, with the exception of a small part at the upper end. The posterior two-thirds join the 

 posterior layer of the deep fascia of the forearm, reaching near to the lower end of the ulna on the 



