330 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



below where it extends between the ribs. Toward the anterior 

 region, where the ribs become shorter and finally vanish, this portion 

 diminishes in breadth, the most anterior fibres being few in number 

 and inserted into the under surface of the transverse processes of the 

 2nd and 3rd vertebrae. 



The fourth portion is broad anteriorly, diminishing rapidly 

 behind. Its fibres anteriorly extend between the lower extremi- 

 ties of the ribs and myocommata ; posteriorly between the corres- 

 ponding portions of the myocommata of the tail. The myomeres 

 have a direction downwards and forwards, so that they are at an 

 angle with those of the third portion. Anteriorly and below the 

 portions of opposite sides are in contact, owing to the absence in that 

 region of the fifth portion, and form a broad, stout muscle, which 

 may be called the ' great ventral muscle.' The posterior fibres 

 run directly forwards, those arising from the anterior shorter ribs 

 downwards as well, so that there is formed between the anterior 

 fibres of the third portion and those of the fourth a triangular 

 space, the base of which is formed by the supraclavicle. Its floor 

 is formed by a dense membrane, immediately below which is the 

 swim-bladder. Anteriorly this portion is attached to the posterior 

 border of the clavicle and to the posterior portion of the lower sur- 

 face of the coracoid, so that, besides assisting portions two and three 

 in bending the body laterally, it acts as a retractor of the 'pectoral 

 arch. The median ventral portion is inserted by an aponeurosis into 

 the posterior cartilaginous arch of the pelvis, forming Owen's pro- 

 tractor ischii, the more external fibres bending slightly outwards and 

 inserting into the posterior angle of the pelvic bone. 



The fifth portion corresponds to Owen's infracarinalis, and Cuvier's 

 muscle grele inferieur du tronc. It consists of two portions separated 

 by the anal fin. The anterior moiety extends from the posterior 

 cartilaginous arch of the pelvis to the base of the anterior ray of the 

 anal fin. This Owen calls the retractor ischii, from its function of 

 pulling the pelvis backwards after it has been drawn forwards by the 

 fourth portion ; in addition to this it has also the power, when the 

 pelvis is fixed, of separating the rays of the anal fin. The posterior 

 half extends between the posterior ray of the anal fin and the caudal 

 fin, and draws the rays of the former backwards, aiding in their 

 separation. These portions arise, similarly to the supracarinalis, 

 from the extremities of the hsemal arches. 



