294 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
hypopharyngeal being attached to the 5th arch, while the epipharyn- 
geal is in relation to the 3rd and 4th arches. <A stronger proof of 
this fact, however, is afforded by a study of the development of these 
bones. They are then seen to be originally quite distinct from the 
adjacent cartilaginous branchial arches, and to be formed by the 
union of the cement-plates of the teeth which they bear, and by a 
subsequent formation of osseous trabecule by osteoblasts. Their 
morphological significance is not hard to determine. They represent 
the remains of the dermal denticles which originally lined the mucous 
membrane of the buccal and branchial cavities, and which are still 
to be seen in those situations in certain Selaclii’. 
V.—THE SPINAL COLUMN. 
With regard to this portion of the skeleton, the greatest interest 
centres round the first four vertebrze and their arches, which have 
become very much modified in accordance with the development of 
a series of ossicles within the auditory apparatus and the air-bladder. 
These anterior vertebre being thus intimately connected with the 
auditory sense-organ, will, ‘with greater appropriateness be described 
in detail in the portion of this work, by Professor Wright, referring 
to that structure. It will be necessary, however, to denote here 
briefly the modifications undergone. The body of the jirst vertebra 
is fully formed, but its transverse processes are rudimentary, while 
its dorsal arch forms the stapes of either side, and a pair of inter- 
crural cartilages present in front of it, are converted into the claws- 
tra. The body of the second vertebra has entirely disappeared, and 
become fused with the third, the fusion being indicated by two 
nutritive foramina at the base of the conjoined vertebre. Its trans- 
verse process is wanting, and its dorsal arch becomes converted into: 
the rudimentary incus. The body of the third fuses with the second 
and fourth ; its dorsal arch is normal, and its spine is represented by 
_ the anteriorly directed process, which, arising from the broad flat 
plate mentioned below, extends forwards and articulates with the 
supraoccipital and exoccipitals ; and its transverse process is trans- 
formed into the malleus. The fourth vertebra is fused with the third 
and fifth ; its transverse process is the broad plate extending out on 
either side in this region, and its dorsal arch is the backwardly pro- 
10. Hertwig Ueber das Zahnsystem der Amphibien. Arch. fiir mikr. Anat. Bd. XI. supple- 
ment 1874. See also Jenaische Zeitsch, Bd. VIII, 1874. 
