336 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



prof. Davidoff l in his valuable papers on the pelvis and pelvic mus- 

 culature of fishes, treats the Teleostei very summarily, merely stating 

 that the differences in musculature and innervation between the 

 Teleosts and Lepidosteus, or, more especially Amia, are quite unim- 

 portant. In comparing Amiurus with his descriptions of either of 

 the two forms mentioned, although the ground-plan is much the same 

 yet the details are much simpler, it being impossible in Amiurus to 

 distinguish, for instance, in the ventral musculature a pars 7iiedia, or 

 in the abd. prof, a caput longum from a caput breve. The names em- 

 ployed above for these muscles indicate their equivalency with those 

 of the pectoral arch. 



IX.— MUSCLES OF THE DORSAL FIN. 



Owing to the modifications of the anterior rays of the dorsal fin in 

 Amiurus, their muscles are also modified. Those of the Jive posterior 

 rays have a typical arrangement. The extrinsic muscles are two in 

 number, namely, the anterior superior fibres of the upper portion of 

 the lateral musculature, which pass from the su preoccipital to the 

 anterior portion of the plate which supports the defensive ray, and 

 will have little or no action in moving the fin, and the supracarinales 

 which will depress the rays. 



Of the intrinsic muscles there are two to each ray, an erector and 

 a depressor. The typical arrangement of these may be seen in the 

 posterior five rays. In these each erector lies anterior to the depres- 

 sor, and arises from the posterior border of the interspinal of the pre- 

 ceding ray. The depressors arise from the anterior border of the in- 

 terspinal of the ray to which each belongs, and from the spinous pro- 

 cess of the vertebra which supports that ray ; each crosses its 

 interspinal obliquely above so as to lie behind it. The erector is 

 inserted into the anterior and the depressor into the posterior surface 

 of the base of each ray. 



Of the muscles of the next anterior ray, i.e., the fourth* the di 

 pr'essor is normal in its relations, arising from the anterior surfa/ ~tt- e 

 the fourth interspinal and the extremity of the spinous process ^ty/ 

 sixth vertebra, and, crossing over the interspinal, is inserted iuv&A 



1 Davidoff— Beitr. zur vergl. Anat. der hinteren Gliedmasse der Fische, ii. Th. Morph. Jahrb. 

 vi , 1880. 



2 This will be the third apparent ray, the first having lost all its ray-like appearance. See 

 paper on Osteology. 



