806 KEPORT OF COMMISSIONER OF FISH AND FISHERIES. [60J 



pital. The body of this latter bone makes up the major portion of the 

 quadrate surface, upon this aspect of the cranium, contained between the 

 spur-like epiotics and the facets of the exoccipitals. Beyond this sur- 

 face the pterotics project on either side, in about the same horizontal 

 l)lane with the superior circumference of the foramen magnum. 



An inferior view of the cranium presents principally for our inspec- 

 tion the two bones, parasphenoid and vomer (Fig. 27, Pr. iS. vomer not in 

 sight). These, as we well know, are in the adult bass, azygos bones 

 lying in the median plane. The paraspJienoid, by the assistance of the 

 basioccipital, forms a large oval-shaped surface beneath the canal for 

 the eye muscles 5 it then contracts again, at which contraction it throws 

 up on either side a plate-like process that has been nearly entirely ab- 

 sorbed by the prootic. The bone beyond this shows another dilation, 

 but not as large as the rear one. It then contracts to form the solid bar 

 that lies between and beneath the orbits (Fig. 27, Pr. 8.), which anteri. 

 orly runs above the vomer and under the prefrontals. 



The vomer of Micropterus is a very i)rominent bone. It is carried 

 back well on the under surface of the paraspheuoid in a pointed proc- 

 ess, the suture between the two bones being easily distinguishable, 

 although this part of the vomer in other respects appears like an ex- 

 tension of the paraspheuoid. Anteriorly it forms a beak which is 

 rounded in front, carried well below the general surface beneath, the 

 inferior aspect of this latter part being semicircular in outline and 

 thickly studded with fine teeth. 



Of a few of the general points to be noticed about the cranium of 

 Micropterus., we have the raised pedicle on the line extending from the 

 prefrontal to the vomer. This pedicle supports an articular facet, di- 

 rected downwards and forwards, for articulation with a rounded and ele- 

 vated facet on the anterior end of the maxillary. The bone I have called 

 supraethmoid in Fig. 27 is so termed by Parker in his Salmon's skull, 

 because it overlies the cartilaginous ethmoid in that fish ; the element 

 is, however, generally termed the ethmoid, or the medium ethmoid 

 (Gegenbaur), and I feel myself at liberty to apply either name to it.- 

 The ethmoid is a very projier one. In this bass the prootics form the 

 anterolateral walls of the eye- muscle canal, but do not meet below in 

 the median line, as thej^ do in some of the Teleostei. Between thera in 

 the median line, and springing from the floor of the brain- case, we find 

 a delicate arch of bone, with its convexity directed forwards, that 

 comes down to meet the paraspheuoid. This arch belongs to the 

 basisphenoid (Fig. 27, jB. S.) and is found in many of the bony fishes. 



As the relations of many of these bones, described above, on the 

 inner cranial wall, show very well in a vertical, longitudinal section of 

 the cranium of our common American perch {Perca americana), I figure 

 such a section here in preference to Micropterus, where the bound- 

 ing lines or sutures among the elements are not so evident or easily 

 studied. 



