40 BULLETIN OF THE BUREAU OF FISHERIES. 



ADDUCTOR ARCUUM BRANCHIALIUM, POSTERIOR. 



The posterior adductor muscle arises on the internal surface, i. e., median, of the 

 bony plate of the fourth epibranchial just within the origin of the preceding. It is 

 inserted into the external surface of the cartilaginous cap of the fifth ceratobranchial. 



TRANSVERSI DORSALIS, ANTERIOR. 



This thin and slightly developed muscle arises from the postero-dorsal surface of the 

 second pharyngobranchial near its junction with the corresponding epibranchial. It 

 runs to a similar attachment on the other side. It is one of the few unpaired muscles. 



TRANSVERSI DORSALIS, POSTERIOR. 



This unpaired muscle is much more strongly developed than the preceding. It 

 arises from the dorsal surfaces of a part of the fourth pharyngobranchial and the dorsal 

 margin of the central end of the fourth epibranchial. The fibers run to similar attach- 

 ments on the other side of the body. 



Some fibers arise on the dorsal surface of the fifth ceratobranchial and become con- 

 tinuous with the constrictors of the pharynx. 



VENTRAL BRANCHIAL ARCH MUSCLES. 



The ventral muscles of the branchial arch consist of three groups, the interarcuales 

 ventrales, the transversi ventrales, and the pharyngo-claviculares. 



INTERARCUALES VENTRALES OBLIQUI (vETTER). 



A group of more or less distinct muscles corresponding to the interarcuales dorsales 

 is present on the ventral side of the branchial basket. In the salmon the anterior three 

 of these muscles are distinct and separate and not divisions of one sheet as in the dorsal 

 group. The posterior two are intimately united. Their dissection should follow that 

 of group E. They are exposed better beginning with the anterior one of the group. 



First division. — The most anterior or first division belongs to the first arch. It is 

 a comparatively small slip which has its origin from the ventral surface of the first 

 basibranchial. It extends along the under surface of the hypobranchial to an attach- 

 ment into the cartilage and ventral tip of the ceratobranchial near its union with the 

 hypobranchial. 



Second division. — The second division arises from the ventral surface of the second 

 basibranchial. It runs its course over the second hypobranchial and is attached by a 

 short strong tendon into the ventral surface of the second ceratobranchial. The first 

 and second arch muscles are completely separated at their area of origin. A tendinous 

 band runs over the ventral surface of the basibranchials between the two slips. 



Third division. — The third division or muscle of the third arch arises from the 

 third basibranchial and the median portion of the ventral surface of the hypobranchial. 

 Its attachment on the third arch corresponds to that of the first and second divisions. 



Fourth division. — This division is continuous with the fifth. They arise from the 

 third basibranchial on the ventral surface somewhat median to and in close contact 



