292 REPORT—1846. 
only the nerve-trunks to be protected by the nasal neurapophyses. These 
are, therefore, more approximated, and the antericr termination of the neural 
canal is much contracted; and, in the tailless batrachia, the nasal neur- ’ 
apophyses coalesce together. 
We recognise in that element (20) of the fourth or foremost inverted arch 
of the crocodile’s skull, which is in connection with the body (vomer, 13) and 
descending plates of the neurapophyses (prefrontals, 14) of the nasal vertebra, 
the proximal or pleurapophysial element of such arch; and the same repe- 
tition of the characteristic connections of the bone, 20, which enabled Cuvier 
and Geoffroy to recognise its special homology with the palatine bone in the 
fish, establishes its claim to be equally regarded in the crocodile as the pleur- 
apophysis of its vertebral segment; although it now affords but a partial at- 
tachment to the bone 21, which forms the next element of the inverted arch. 
This bone, the hemapophysis, has undergone a striking change in its propor- 
tions by development both in length and breadth: it is connected not only with 
no. 20 behind and with no. 22 before, but with the elongated spine, no. 15, of its 
own vertebra, and with the lacrymals, 73, above ; with its fellow of the opposite 
side below, and with a well-developed proximal element, no. 26, of a strong 
diverging appendage behind. The hemal spine, no. 22, is divided, and the 
arch is completed by the symphysial junction of the two halves at Hiv. The 
nasal aperture or entry to the air-passages forms the span or area of the 
much-modified inverted arch constituting the upper jaw of the crocodile. 
The two proximal elements of the arch, nos. 20 and 21, continue to send 
outwards and backwards exogenous diverging processes; but they consti- 
tute a smaller proportion of the bones than in fishes, and both processes di- 
rectly support distinct bones representing the diverging appendage of the 
arch, and serving to fix and attach it to the succeeding arch. The pleurapo- 
physial appendage (pterygoid, 24) soon coalesces, however, with its fellow 
and with the centrum of its own vertebra (vomer, 13), and then expands to 
unite by a broad sutural surface with the coalesced centrums of the frontal 
and parietal vertebre (9 and 5). A second osseous piece (ectopterygoid, 
24’) diverges from the pleurapophysis external to the preceding and attaches 
it to the hemapophysis, to the heamapophysial appendage, and to the par- 
apophysis of the frontal vertebra. The strong diverging ray from the hem- 
apophysis is teleologically subdivided into nos. 26 (malar) and 27 (squamosal), 
and firmly attaches the maxillary arch to the pleurapophysis (28) of the man- 
dibular one. 
In the chelonian reptiles the modifications of the nasal segment of the 
skull adhere pretty closely to the type of those in the crocodile; the centrum 
is more independent and better developed, but the divisions of the neural 
spine have coalesced with their neurapophyses: the diverging appendages, 
a6 and 27, are usually developed into broad and flat bones. In many lizards 
we find the nasal centrum divided but the neural spine single: the hemal 
spine is, also, single, as a general rule, and sends upwards and backwards a 
process to join the neural spine, divide the area of the hemal canal, and 
terminate the vertebral series anteriorly. The hemapophysial diverging ap- 
pendage commonly resumes its long and slender ray-like proportions, and joins 
the parapophyses of both frontal and parietal vertebre as well as the prox- 
imal end of the pleurapophysis of the mandibular arch. In serpents both 
divisions of this appendage are absent (indicating the inferior character of 
the bones 26 and 27 in general homology), but the two parts of the pleurapo- 
physial appendage, 21 and 24', are retained and serve as levers in the move- 
ments of the maxillary arch. The spine of that hemal arch is single, and 
commonly united only by lax and elastic ligaments with the hemapophyses, 
