"254 MR, E. p. ALLIS ON THE OTIC REGION OF 



operculi, in contact with it, and to all appearance a part of it, 

 but it is inserted in part on the dorsal end of the supraclavicula 

 and in part in the dermis that forms the dorsal corner of the gill- 

 opening. The distal portion of this muscle is quite certainly 

 innervated by the ramus opercularis facialis, and is hence a 

 derivative of the levator opercali, and it has acquired entrance 

 into the temporal groove by passing upward external to the 

 posterior process of the pterotie. This suggests a secondary 

 rather than a primary arrangement, and leads one to suppose 

 that the groove was primarily developed in relation to an invasion 

 by the trunk-muscles, and that the dovso-mesial portion of the 

 muscle that actually occupies the groove has, possibly, been 

 derived fi-om a portion of the trunk-muscles that was cut off 

 from the parent muscle by the peculiar attachment of the 

 supraclavicula. In favour of this assumption are the facts that 

 this dorso-mesial portion of the muscle seems to be in a somewhat 

 disintegrated condition, that the groove here contains considerable 

 fatty tissue, and that, in certain other fishes (Ainia, Allis, '97, 

 p. 567), the levator opei'culi does actually invade a temporal 

 groove already occupied by an anterior extension of the trunk- 

 muscles. Furthermore, the position of the epiotic, somewhat 

 removed from the dorso-postero-latera.1 corner of the cranium, 

 would seem to indicate that the trunk-muscles had, in the 

 ancestors of this fish, occupied the temporal groove. It is, 

 however, to be noted that, even in a 57 mm. specimen of 

 Galostomus occidentalism which I ha.ve examined in serial sections, 

 iihis muscle has no slightest connection with the trunk muscles. 



In Ameiarus, McMurrich ('84) describes a cavity enclosed 

 between the pterotie, epiotic, and supraoccipital bones, which he 

 says is, in all probability, a rudiment of the temporal fossa of 

 Sagemehl's descriptions of Amia. It is said to contain only fatty 

 tissue, and its opening is said to be almost closed by the supra- 

 ■clavicula,. The supraclavicula is said to be " a T-shaped bone, of 

 which the upper portion of the transverse limb articulates with 

 the pterotie and epiotic, and almost occludes the opening of the 

 temporal fossa, while the extremity of the vertical limb articulates 

 with the side of the basioccipital." I have shown, in an earlier 

 work (Allis, '04), that the superficial portion of the transverse 

 limb of this bone is ti'aversed by the main latero- sensory canal, 

 and this led me to call the entire bone the suprascapula. The 

 bone has a mesial limb which was said by me to lie in a, vertical 

 plane, its anterior surface resting against the hind edge of the 

 dorsal surface of the cranium, and its ventral edge partly upon 

 the epiotic and partly upon a bone which I considered to be a 

 greatly reduced parietal. The relations, to the cranium, of this 

 mesial limb of this bone of Amehtrus thus strongly resemble 

 those of the dorsal end of the supraclavicula of Moxostoma, 

 provided that the parietal bone of my descriptions of Ameiurus 

 is the so-called suprascapula of Moxostoma, which seems highly 

 probable. It must then be that the supi'ascapula of Amia and 



