392 Proceedings of the 



dify the pressure of blood on the head according to the pres- 

 sure of water upon the fish. 



Muscular System. 



The muscles of mastication of the Malapterurus are remark- 

 able in their relation to the eye. By much the largest mass 

 arises from the whole roof of the skull> as far forwards as the 

 anterior extremity of the great frontal bone, and passes over 

 the optic nerve and muscles of the eye in its course to the 

 articular piece of the lower jaw, into the upper angle of which 

 it is inserted. The eye-ball is situate at its external border. 

 Another mass arises from the upper surface of the tympanic 

 bones, and is inserted along with the preceding ; it is smaller, 

 and lies below the eye. Another and slender muscle is 

 attached anteriorly to a process on the superior maxilla, and 

 behind, to the epi-tympanic bone. Thus the structures to the 

 eye-ball, as well as the divisions of the fifth nerve, pursue 

 their course between two great masses of masseter muscle. 



The transfer salis palati muscle arises from the under 

 surface of the basi-sphenoid and anterior frontal bones and the 

 inter-orbital septum, and its fibres pass transversely outwards 

 to the under surface of the ptery go-tympanic arch. The 

 mylohyoid arises from the upper half of the hyoid arch, and is 

 inserted in the whole length of the dental piece of the lower 

 jaw. A muscle arises from the posterior border of the hyoid 

 arch and from the inferior branchiostegal rays, and its fibres, 

 passing transversely inwards, are inserted in the middle line 

 on the under surface of the urohyal bone, which it is calcu- 

 lated to elevate, and it must therefore act as a muscle of de- 

 glutition. The so-called sternohyoid muscle passes from the 

 posterior border of the urohyal bone backwards to the cora- 

 coid bone, and lies near its fellow of the opposite side. 



The muscles of the operculum are three: one arises from the 

 orbito-sphenoid and anterior part of the post-frontal bone, and, 

 passing beneath the long process of the post-frontal, receives 

 additional fibres from the lateral margin of that bone, and is 

 inserted into the superior angle of the operculum, and acts as a 

 levator. Another arises from the side of the mastoid bone, and 

 is inserted into the upper part of the posterior margin of the 



