78 
PEOFESSORS T. W. BRIDGE AND A. 0. HADDON 
while the posterior ridge, which is really the intracranial prolongation of the neural 
plate of the exoccipital, looks directly forwards. Each recess is prolonged backwards 
to the outer side of this portion of the exoccipital until it becomes closed behind by 
the posterior plate of the same bone and by the epiotic. (See transverse section of 
this part of the skull in fig. 7.) 
In places the outer walls of the auditory capsules are extremely thin, and this is 
notably the case where they are formed by the epiotic and prootic bones and by the 
opisthotic plates of the exoccipitals. Over definitely circumscribed areas these bones 
are almost transparent when the skiill is held up to the light. 
Although foreign to the subject of this paper, it may be mentioned that at each 
postero-lateral angle of the skull there is a deep fossa, closed internally but open 
externally, and formed by the opposition of correlated grooves in the pterotic and 
epiotic in front and behind respectively, and by the supraoccipital internally and 
superiorly (figs. 1, 4, and 6, tp.f.). Eamsay Wright (43), in his description of the 
skull of Amiurus catus, throws out the suggestion that these fossm may be the 
atrophied rudiments of somewhat similar cavities described by Sagemehl'^' as present 
in Amia calva, and by him termed the temporal fossse. In Macrones each fossa 
fulfils the function of an articular cavity for the proximal extremity of the ascending 
process of the post-temporal (fig. 6). 
The Pectoral Girdle. — The post-temporal (supra-clavicle of Eamsay Wright and 
others) is the only element of the shoulder-girdle that, for our purpose, requires any 
special description. 
As in most other Teleostei, the post-temporal is somewhat V-shaped, its two 
divergent arms articulating with the postero-lateral angle of the skull and its stem 
with the proximal extremity of the clavicle (figs. 3 and G). Of the two arms, one, 
the ascending process, is somewhat loosely inserted into the temporal fossa of its side 
(fig. Q,pt.a.), while the other, or inferior limb (pt.i.), articulates by a doubly-facetted 
step-like inner extremity with a pair of suitably modified processes on the lateral 
surface of the basioccipital. Externally the two processes converge, and eventually 
unite to form the post-temporal stem (fig. 6 , pt.s.). The latter is a flattened process 
of bone continuous superiorly with the ascending process, and so superficially situated 
that its outline is readily seen on the external surface of the body behind the posterior 
edge of the operculum (fig. 15, ^9^.). From the inner surface of the stem, and also 
from the adjacent ventral margin of the inferior limb, a relatively thin, transversely- 
disposed plate of bone grows downwards, and is so arranged that its two surfaces look 
directly forwards and backwards respectively (figs. 3 and 6, p)^-P-)- posterior 
face of each plate is comparatively smooth, and at the same time faintly concave, and, 
moreover, is so applied to the crescentic extremity of the anterior division of the 
transverse process of the fourth vertebra as to fill up the concavity of the latter, and 
* “ Beitrage zur vergl. Anat. der Fisclie. Das Cranium von Amia calva." ‘ Morpliol. Jahrbuch, 
vol. 9, 1883. 
