The Lateral Sensory System in the Muraenidae. 143 



surface in the normal condition of rest. The 5*^ pore lies in the 

 transverse plane of the anterior edge of the eye, and is always found 

 on the ventral, or labial side of the maxillary furrow, near the upper 

 edge of the maxillary labial fold. The furrow is here shallow, and 

 the pouch that leads inward from the pore passes upward internal to 

 the furrow to reach its canal. The two anterior pouches also lie in 

 part internal to the furrow, though their surface openings lie dorsal 

 to it. All these pouches are somewhat folded upon themselves because 

 of their relations to the furrow, and the fourth pouch has peculiar 

 relations to the maxillary labial fold. This pouch occupies a large 

 oval bay in the lachrymal, and is covered externally by only a thin 

 layer of dermis which lines the bottom of a pit-like depression that 

 forms the deepest part of the maxillary furrow. Into this depression 

 fits a pad-like eminence on the inner surface of the maxillary fold, 

 and pressure here forces fluids out of neighbouring pores of the infra- 

 orbital canal. I have not yet been able to make out how this pres- 

 sure could be applied voluntarily by the fish, but it would seem as 

 if the purpose of the arrangement must be to give the fish some 

 control of the circulation of the fluids in the canal. The large pouches, 

 some of them blind, in other parts of the lateral system, lying as 

 they to immediately beneath the skin, must also contribute to this 

 control. 



The 6*^ pore of the line lies at a short distance from and almost 

 directly posterior to the angle of the gape of the mouth. It leads 

 upward into the postero-ventral portion of a long pouch which arises 

 from the main canal at the angle where it turns upward behind the 

 eye. The three pouches dorsal to this one are long and blind, and 

 extend directly backward from the postorbital part of the canal, lying 

 betAN'een the outer skin and the external surface of the muscles of 

 the cheek. 



Dorsal to tube Xo. 9 the infraorbital canal becomes immediately 

 enclosed in fibrous tissue, and this tissue is supported, along its anterior 

 and dorso-posterior surfaces, by processes of cartilage which project 

 from the adjoining osseous side wall of the skull. The bases of these 

 Itrocesses are more or less ossified, the cartilaginous processes thus 



