738 MR FEANK J. COLE 



(cp. also fig. 13, 4), part of the fibres passing straight downwards, internal to the 

 posterior section of the tract, to assist in forming the inner portion of the ventral 

 insertion (8), and the remainder coursing backwards, immediately dorsal to the other 

 fibres of the inner portion of the insertion, and forming a bundle which remains distinct 

 from the latter up to about 3078, but which then merges into it. 



The Fifth Loop (5) separates itself from the inner surface of the posterior external 

 sheet of the constrictor opposite the middle of the last gill, and passes in a curve down- 

 wards and slightly backwards. It finally bifurcates into a short postero- ventral division, 

 which penetrates between the posterior extension of the anterior section of the ventral 

 tract and the remaining fibres of the inner portion of the ventral insertion to terminate 

 on the internal fascia of the latter without reaching the ventral insertion, and into an 

 anteriorly directed division. This latter constitutes the posterior section of the ventral 

 longitudinal tract {7'), which courses forwards immediately under the anterior section, 

 but which, except for a few connecting fibres, as shown in the Chart, is quite distinct 

 from it. The posterior section terminates anteriorly on the internal or dorsal surface of 

 the rectus muscle. On the right side the fifth loop splits as above stated, but the 

 posterior division bends downwards and forwards, and forms the most anterior bundle 

 of the inner portion of the ventral insertion. 



The above facts show that the ventral longitudinal tract is not a definitive muscle, 

 but is rather a complex, formed of the secondarily juxtaposed contributions from about 

 three loops 4- other fibres, as above described. 



The Sixth Loop (6), which is smaller than 1 found it in dissections, is detached from 

 the internal surface of the posterior external sheet of the constrictor, and passes almost 

 straight downwards to its insertion. This represents the outer portion of the ventral 

 insertion (8 r ), but it differs very considerably from the insertion as I found it in 

 dissections. In the first place, it is not only absolutely distinct from the inner portion, 

 but entirely posterior to it. Then only two small bundles pass inwards and downwards 

 between the two recti muscles at the mid-ventral line in the normal manner, most of 

 the fibres being inserted into the lateral or outer margin of the left rectus. Posteriorly 

 it receives the small special constrictor of the ductus cesophago-cutaneus {14), as above 

 described. 



On the right side the sixth loop is very reduced. It is continued from the ventral 

 border of the posterior external sheet of the constrictor slightly below the ventral margin 

 of the parietalis and at the transverse level of the posterior outline of the last gill. It 

 then courses obliquely downwards and forwards, to be attached to the lateral margin of 

 the right rectus. There is thus only a slight outer portion of the ventral insertion on 

 this side. In dissections I have sometimes not found the sixth loop on the right side 

 at all, and hence the outer portion of the ventral insertion may in some cases be entirely 

 wanting on this side. 



The inner portion of the ventral insertion (8) is formed partly by fibres from the 

 third and fourth loops ( + the fifth on the right side), but largely by the definitive fibres 



