192 Scientific Proceedings, Royal Dublin Society. 



The pectoral fin consists of about nineteen rays, each of wliioh. 

 is composed of two pieces firmly united together. These diverge 

 at the base, and include within them a strip of cartilage, which is 

 connected to the glenoid facet of the scapula and to the three 

 radialia and the metapterygial basale. Ai their basal ends the rays 

 are somewhat expanded, and present a double row of tubercles. 

 Those of the inside (for the insertion of the double row of the 

 tendons of the adductor . muscles of the fin) are more largely 

 developed, and lie farther apart than the outer ones. The latter 

 are for the abductor muscles, and lie close together. The rays are 

 marked with transverse constrictions, especially near their distal 

 extremities. They continue as single rods for more than half their 

 length, and then split loDgitudinally into halves, which show a 

 further tendency to divide at their distal extremities. This cleav- 

 age is at right angles to the line of union of the two primary 

 pieces of which each ray is composed. The first or anterior ray is 

 very short, not more than half the length of the fin, but is the 

 strongest of all. They increase in length up to the sixth, which 

 is the longest. After this they diminish, the last two or three 

 being very short and almost rudimentary. 



Ligamentous fibres hold the limbs of the post-temporal in 

 place, and a strong rounded ligament keeps the upper end of 

 the clavicle from displacement backwards ; it is attached to the 

 postero-internal border of the -supra-clavicle, and winds behind 

 the superior process of the clavicle, piercing the lateral muscles, 

 and notching the kidney, to be attached to the atlas in the manner 

 above described. 



The pelvic bone is similar in structure to the coracoid. It pre- 

 sents a thickish, triangular portion (PL IX., fig. 26, a), whose free 

 border, slightly curved, looks outwards and slightly backwards. 

 To this is attached a strip of cartilage, which supports the fin-rays. 

 A rod-like portion, h, is attached to the inner angle of the above- 

 mentioned piece, and stretches forwards and inwards, to be united 

 with its fellow of the opposite side by cartilage, forming with it an 

 angle of about 115°. This lies in the angle formed by the lower 

 ends of the clavicles, and is connected to the latter by ligamentous 

 and muscular fibres. A smaller flattened rod, c, passes backwards 

 and inwards from the junction of the other two. Thin laminae of 

 bone connect these three pieces together. 



