GREGORY: FISH SKULLS 385 



ends of the cross-bars, i.e., from the postorbital processes (presumably of the frontals) 

 starts a broad, backwardly-pointing V, the limbs of which are low ridges that are more or 

 less distinctly outlined in the cranial roof; the apex of this V is the posterior end of the 

 occipital crest. Another V, pointing in the opposite direction, starts from the backwardly- 

 projecting tips of the epiotics and runs forward, crossing the first V and having its tip at the 

 junction of the cross-bar and the stem of the T. Still another V, with less divergent but 

 very prominent limbs, lies on the surface of the interorbital constriction, its apex meeting 

 the cross-bar of the T in the mid-line. The dorso-lateral surface of each of the widely- 

 projecting hyomandibulars also bears a well defined but irregularly V-shaped crest; the 

 apex of this lies above the stout pedicle for the opercular, the anterior limb runs up to the 

 anterior or sphenotic head of the hyomandibular, the posterior limb of the V surmounts 

 the posterior or pterotic head of the hyomandibular. So too in the inferior aspect of the 

 skull one can readily distinguish two large and oppositely-pointed V's: the backwardly- 

 pointed one has its limbs running obliquely across the prootic, its apex slightly truncated 

 at the occipital condyle. The forwardly-pointing V has its apex under the parasphenoid; 

 its sides are the diverging prootic borders of the braincase. In the occipital view of the 

 skull the occiput itself is distinctly V-shaped, although its downwardly-pointing apex is 

 rounded. From the limbs of this large inverted V diverge two small, more widely open 

 triangles, whose legs touch the pterotics and supraoccipital respectively, and whose bases 

 are formed by the fiat skull. 



This plethora of geometric and even Masonic designs in the skull of a fish which might 

 well have been called the triangle-fish, besides affording a capital example of "Unnatural 

 History Resemblances," to add to those cited by Dean (1908), may well excite our wonder 

 even though we believe that these geometric figures are but the latest and most refined 

 product of the selectively eliminative effect of Nature operating upon that well known- 

 property of bony tissue that gives it the power to thicken itself and develop trabeculae along 

 the lines of greatest stress. But to put the proposition the other way around, in order that 

 the lines of greatest stress should conform to a system of opposing V's, it was necessary that 

 the forces of growth, muscular contraction, water pressure, etc., should themselves be so 

 orientated, at such positions and angles with reference to the main axes, as to produce the 

 observed results. 



No doubt the special patterns of a particular fish skull have grown out of the general 

 symmetries and basic patterns of all fish skulls, e.g., the invariable antero-posterior sequence 

 of the three main sense-capsules, the fundamental vertebrate relations of antero-posterior 

 polarity, of bilateral symmetry and of the dorso-ventral sequence of neuron, notochord and 

 enteron. But in the special case under consideration the dominant factor in the formation 

 of the whole complex of interrelated V-like ridges in the skull of the common toad-fish ap- 

 pears to be the spreading apart of the opposite quadrate-articular joints and the consequent 

 increase of transverse wrenching stresses and strains due to the increased transverse leverage 

 of the powerful adductor mandibulae muscles, especially since the thrusts of the inwardly 

 directed teeth of the mandible have strong transverse components, which would tend to 

 dislocate a weakly braced palatopterygoid arch. In fact, inspection shows that nearly 

 all the V-shaped crests have plainly discernible relations to the wrenching strains from the 

 mandible, which are relatively much greater than in fishes in which the mandible has a 

 simple chopping movement. Hence it may not be improbable that many of the above 



