390 Harris Hawthorne Wilder, 



associated with the fibers of insertion of the most ventral slip of 

 M. serratus anterior. The tendon of this muscle is extrem ely difficult 

 to follow to its origin in the occipital bone, and is best seen in a 

 specimen from which the entire floor of the mouth and pharynx, 

 together with the gill arches, has been cut away. The muscle may 

 then be found at its scapular end and followed forward. 



M. serratus anterior (so). This muscle is entirely covered 

 extern ally by the latissimus dorsi, and consists of a series of flat 

 slips (serrations) which arise posteriorly from myocommata, or from 

 the distal ends of the ribs developed in them, and insert anteriorly 

 into the medial (inner) surface of the suprascapula. There are three 

 of these slips, the most ventral one from myocomma 7, the middle 

 one from myocomma 6, and the most dorsal one from myocomma 5. 

 The two anterior of these arise from the cartilaginous tips of the 

 myocommatous ribs; the posterior from the myocomma itself. They 

 insert into the medial surface of the suprascapula in an order cor- 

 responding to their origins. the one from myocomma 7 being the 

 most posterior and so on. The most anterior of these slips becomes 

 associated at its insertion with that of the levator anguli scapulae. 



2. Ventral aspect. 



M. pectoralis (p). This muscle in Necturus is in the form 

 of a Single large sheet, not divided into separate slips or portions 

 as in higher forms. It Covers the entire pectoral region between 

 the fifth and ninth myocommata. Its anterior edge is coincident 

 with the middle fibers of M. supracoracoideus, which it overlaps; 

 and as the fibers of the two have the same general direction at this 

 place, and the pectoralis is very thin here, the two are easily taken 

 for parts of a continuous sheet. 



The origin of the pectoralis is a very extensive one and includes 

 the ventral portion of the ninth myocomma as well as the entire 

 linea alba from the point at which the ninth myocomma meets it 

 as far forward as the point described above, that is, to about the 

 level of myocomma 5. Although this line of origin consists of two 

 parts which meet each other at nearly right angles, the fibers form 

 an uninterrupted series, thus making a continuous sheet of conver- 

 ging fibers. In direction the fibers composing this sheet differ from 

 one another by a little more than 90°; the most lateral of these 

 arising from the myocomma are nearly longitudinal, those crossing 

 the mid-coracoid region are transverse and form a right angle with 



