330 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
below where it extends between the ribs. Toward the anterior 
tegion, 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_ vertebre. 
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 asa 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 gréle 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 hemal arches. 
