TRANSACTIONS OF THE SECTIONS. 141 
is given to the body of the microscope by a simple mechanical arrangement. The 
stage-trough containing salt-solution is warmed by a very simple hot-water 
apparatus, the temperature being registered by a stage-thermometer in the usual 
manner. 
“ 
Preliminary Notice of an Inquiry into the Morphology of the Brain and the 
Function of Hearing. By Professor Cretanp, Galway. 
In this paper it was demonstrated that the flocculus is a lateral projection from 
the third cerebral vesicle, and that the optic thalami are not developed in the first 
cerebral vesicl® but in the constriction between it and the second. The author’s 
hypothesis is, that the cerebral hemispheres are derived from the front of the first 
cerebral vesicle by a process of longitudinal fission, similar to that which he had 
formerly shown to take place in other cephalic structures (Phil. Trans. 1862), 
that the primary optic vesicles have a closer connexion with the second than with 
the first cerebral vesicle, and that the olfactory bulbs, optic vesicles, and floceuli 
are serially homologous; and he judges that the flocculi are connected with the 
sense of hearing. 
Observations, with Graphic Illustrations, on a pair of Symmetrical Bones pre- 
sent with the Fossil Remains of Iguanodon. By W. Warernousr Hawkins, 
F.LS. 
Note on the Development of the Columella Auris in the Amphibia. 
By Professor T. H. Huxtey, F.B.S, 
In his paper “On the Structure and Development of the Skull of the Common 
Frog ”’ (Phil. Trans. 1871), Mr. Parker states that, in the fourth stage of the tad- 
pole*, “the hyoid arch has made its second great morphological change; it has 
coalesced with the mandibular pier in front and with the auditory capsule above 
(plate v. figs, 1-4, and plate vi. fig. 8, s.h.m., i.h.m.). The upper part, or suprahyo- 
mandibular (s.h.m.), is attached to the auditory sac much lower down and more 
outward than the top of the arch in front. . . . . This upper distinct part is 
small; it answers to only the upper part of the Teleostean hyomandibular; there 
is a broad sub-bifid upper head answering to the two ichthyic condyles, then a 
narrow neck, and then behind and below an ‘opercular process’ (op.p.). Below 
this the two arches are fused together; but the hyoid part is demonstrated, just 
above the commencement of the lower third, by the lunate fossa for the ‘styloid 
condyle’ (plate v. figs. 2 & 4, st.h.).” (pp. 154, 155.) 
In the sixth stage “the ‘suprahyomandibular ’ (fig. 3, s.hm.) has become a free 
plate of cartilage of a trifoliate form” (p. 164). 
In the seventh stage “the ‘suprahyomandibular,’ losing all relation to the 
hyoid arch, becomes now part of the middle ear. . . . The essential element of the 
middle ear, the stapes (s¢.), was seen in the fourth stage; the condyles and oper- 
cular process of the hyomandibular are now being prepared to form an osseo- 
cartilaginous chain from the ‘membrana tympani’ to the stapes. Under these 
conditions a new nomenclature will be required; and this will be made to depend 
upon the stapedial relationship of the chain, notwithstanding its different morpho- 
logical origin. 
“T shall now call the lobes of this trifoliate plate of cartilage as follows—namely, 
the antero-superior .‘suprastapedial,’ the postero-superior ‘medio-stapedial,’ and 
the freed opercular process ‘extrastapedial’ (s.st., m.st., e.st.). 
“The ee (st.) sends no stalk forwards to meet the new elements, but they 
grow towards it; this will be seen in the next stage.” (pp. 169, 170.) 
As the question of the origin of the columella auris in the Vertebrata is one of 
considerable morphological importance, I have devoted a good deal of time during 
the past summer to the investigation of the development of this structure in the 
frog; and it is perhaps some evidence of the difficulty of the inquiry, that my 
* That is, when there is a branchial aperture only on the left side, and the hind limbs 
are rudimentary or very small. ; 
