42 BULLETIN OF THE BUREAU OF FISHERIES. 



sheet at the insertion into the inner surface of the anterior portion of the dentary around 

 the symphysis. At its insertion the tendon is di\'ided into an external and an internal 

 portion, one passing above, the other below the intemiandibularis to its insertion. 



HYOHYOIDEUS. 



This long thin sheet of muscle arises from the ventral surface of the hypohyal and 

 passes diagonally outward and backward to insertions over the branchiostegal rays. 

 The muscle has attachments to the internal margin of each successive ray. It also has 

 insertions along the ventral margins of the ceratohyal and epihyal. The left hyoideus 

 somewhat overlaps the right at its origin. 



STERNOHYOIDEUS. 



The name sternohyoideus is applied to a broad and thick sheet of muscle arising 

 on the dorsal surface of the anterior end of the clavicle directly in front of the attachment 

 of the pharyngo-clavicularis extemus. Its fibers run forward and are attached to the 

 ventro-lateral surface of the hypobranchial plate. Its differentiation from the ventral 

 portion of the great lateral muscle is apparent and probably it would be better to group 

 it with the longitudinal muscles. 



MUSCLES OF THE CAUDAL FIN. 



The modifications of the musculature which have come about for the control of the 

 movements of the caudal fin are associated with striking modifications of the caudal 

 skeletal structure. In order to present more accurately the form and relations of the 

 muscles it seems desirable to give the facts concerning the caudal skeletal complex. 



CAUDAL SKELETAL COMPLEX. 



The caudal fin in the king salmon is regularly bilobed and symmetrical. Externally 

 it appears of the regular homocercal type. The caudal skeleton, however, still shows the 

 heterocercal structure as presented by figure 5. The skeleton reveals the fact that the 

 epichordal component is limited to the rudimentary rays and at most the first two rays 

 of the dorsal lobe. The remainder of the dorsal lobe and all of the ventral represents the 

 hvpochordal component. This modification rests on a rather complex caudal skeletal 

 base, as was shown by Kolliker "■ for Salmo salar. 



The axial region may be considered as composed of those vertebrae entering into the 

 caudal peduncle, and those of the caudal fin proper. Of the three obvious vertebrae that 

 enter into the caudal fin skeleton one only has a well developed centrum. The second 

 and third centra are very much reduced in size, the latter being only a tiny bony nodule. 

 The modifications of the vertebrae of the caudal peduncle beg^n sharply with the last three 

 vertebrae of the group. However, the spines of the fifth and fourth, counting from the 

 tail, have a median flange on the anterior margin of the neural spines. In the last three 

 vertebrae these flanges are fused each with the spine in front of it. The neural spines 

 of the first and second caudal vertebrae enter into this fusion, the five spines making a 

 firm mass. 



a Kolliker, Albert von: Ueber das Ende der Wirbelsaule der Ganoiden und einiger Teleostier, taf. iv, fig. z and 2. 

 Leipzig, i860. 



