— 174 — 



depression which gives articulation to the dorsal end of a long, slender, gutter-shaped and tapering 

 bone, which is applied to the antero-lateral surface of the dorsal end of the clavicle and is certainly 

 the SUPRACLAVICULAR. This bone is not traversed by the rnain infraorbital canal, and its 

 latero-sensory eornponent must be represented either in a part of the unusually large suprascapular 

 or in a small bone that lies along the postero-lateral edge of the suprascapular and is traversed by 

 the main infraorbital canal after it leaves that bone. 



On either side of the hind end of the skull there is a large and deep fossa, already several 

 times referred to. This fossa occupies the entire posterior surface of either side of the skull, and has 

 deep dorso-mesial and dorso-lateral corners. or recesses, and a shallow ventral one. It is bound^d 

 by the mesial extrascapular, suprascapular, supraoccipital, epiotic and exoccipital, and there is nothing 

 eomparable to it in any of the other fishes of the group. Want of material prevented a proper 

 investigation of it, but it is largely, if not entirely filled by an anterior Prolongation of the swiin- 

 bladder: the dorsal wall of this portion of the bladder lying close against the ventral surface of the 

 dermal bones that form the roof of the fossa, and the lateral surface of the bladder having closely 

 applied to it a band-like anterior Prolongation of the trunk muscles. 



2. INFRAORBITAL CHAIN OF BONES. 



The infraorbital chain consists of four bones, all of which are traversed by the main iufra- 

 orbital canal. In addition to these four bones, there is a small bone, the pontinal of Grill, which extends 

 from the hind edge of the second bone of the series into a reentrant angle on the anterior edge of the 

 preopercular. 



The first infraorbital bone, or lachrymal, has a thickened anterior end which curves mesially, 

 and almost meets, in the middle line, its fellow of the opposite side. The dorsal edge of this part of 

 the bone is slightly grooved and articulates moveably with the antero-ventral edge of the nasal, the 

 dorsal edge of the lachrymal lying upon and being strongly but somewhat loosely bound to the outer 

 surface of the lachrymo-palatine process of the nasal. Internal to the hind end of this grooved 

 portion of the lachrymal, there is, on the internal surface of the bone, a short transverse ridge with 

 a convex outer edge, and slightly posterior to this ridge there is a second but shorter ridge; these 

 two ridges and the groove between them having a sliding articulation with the palatine on the dorso- 

 lateral surface of its maxillary process, as will be later explained. Slightly ventro-posterior to these 

 two articular ridges, a strong brace-like process arises from the internal surface of the lachrymal, 

 projecting dorso-postero-mesially. The dorsal end of this process is large, lies in the level of the 

 dorsal edge of the bone, and has on its dorsal surface a large oval facet which articulates with the 

 lachrymal articular eminence of the ectethmoid. The hind edge of the articular facet suturates with 

 the anterior edge of the orbital shelf of the second infraorbital bone, the hind edge of the lachrymal 

 itself suturating with the second and third infraorbital bones; the second infraorbital lying ventral 

 to the third one and having no bounding relations to the orbit. The bone is traversed by the main 

 infraorbital latero-sensory canal and lodges three sense organs of that line. 



The second infraorbital bone is an elongated one, bounded anteriorly by the first and dorsally 

 by the third bone of the series. The main infraorbital canal enters it at its anterior edge, runs hori- 

 zontally backward in it and then turns upward and forward at an acute angle, to leave the bone on 

 its dorsal margin and enter the third bone of the series; this section of canal lodging two sense 



