— 148 — 



suprascapular. The primary portion of the bone encloses, as usual, the outer portion of the horizontal 

 semicircular canal. On the lateral surface of this part of the bone, near its dorsal edge, is the facet 

 for the posterior articular head of the hyomandibular. Dorso-anterior to this facet, a small pit-like 

 depression forms the posterior half of the dilatator fossa. The posterior process of the bone is relative - 

 ly small, is directed ventro-laterally and but slightly posteriorly, and is in contact with the dorsal 

 edge of the opisthotic. The dermal portion of the bone is traversed by the main infraorbital canal, 

 the section of canal enclosed in the bone lodging one organ innervated by the oticus, and quite 

 certainly, though this could not be positively determined, a second, post-preopercular organ innervated 

 by the supratemporalis lateralis vagi. The primary tubes indicate the presence of two organs here, 

 one tube arising from the canal at the anterior edge of the bone, another at the hind edge of the bone, 

 and a third slightly anterior to the middle of the bone; this latter tube issuing from the bone on its 

 lateral edge, immediately posterior to the facet for the posterior head of the hyomandibular, and anasto- 

 mosing with the dorsal end of the preopercular canal. The post-preopercular organ must, if present, 

 be a small one, for it could not be definitely recognized in any of the dissections, although a branch 

 of the supratemporal branch of the vagus, which nerve contains lateralis fibers, was always found 

 perforating the pterotic, and going to that part of the canal where the organ would be found, 

 if present. 



On the lateral edge of the pterotic, immediately posterior to the opening of the primary tube 

 that anastomoses with the preopercular canal, there is a large, slightly convex surface, marked with 

 Striae. This surface lies on a slightly elevated portion of the bone, lies mainly on the primary portion 

 of the bone, and gives a sliding articulation to the dorsal edges of the united suprapreopercular and 

 hyomandibular. 



The SUPRAOCCIPITAL has dorsal and ventral limbs, the dorsal limb being entirely covered 

 by the frontals and parieto-extrascapulars, excepting only a small median portion of its hind edge. 

 The anterior edge of this limb of the bone bounds the hind edge of the postepiphysial cartilage. The 

 ventral limb of the bone has a prolonged median portion which extends nearly to the dorsal edge 

 of the foramen magnum. This Prolongation of the bone lies upon the external surface of the 

 adjoining edges of the exoccipitals and on the narrow median band of cartilage that separates those 

 bones, thus apparently being of ectosteal origin. In its dorsal portion the ventral limb of the bone 

 expands and is in contact with the exoccipitals and epiotics. In the median line, near the dorsal 

 end of the limb, there is a small vertical ridge which represents the slightly developed spina 

 occipitalis. 



2. INFRAORBITAL BONES. 



The infraorbital bones are five in number, all of them traversed by the main infraorbital canal. 

 The anterior bone, or lachrymal, lodges four sense organs of the line, the second bone one organ, 

 the third bone two organs, and the fourth and fifth bones one organ each. The total number of organs 

 enclosed in these bones is thus nine, that being the total number also in both Tris;la hirundo and 

 T. lyra. The lateio-sensory ossicles are not however interfused in the same manner in either of these 

 three fishes, as the following table will show. The young Trigla lyra, given in this table, is assumed 

 to have six bones in the series, as Günther says it has, and the arrangement of the organs in this fish 

 is hypothetical, as all of my fishes had but five bones. 



