P 
e 
‘ON THE VERTEBRATE SKELETON. 289 
by ‘its restricted functions, and having no call for progressive growth in sub- 
serviency to a branchial respiration. It consists of a ligamentous stylohyal, 
its plewrapophysis, retaining the same primitive histological condition which 
obstructs the ordinary recognition of the same elements of the lumbar hemal 
arches. The hemopophyses and hemal spine are, however, here as there, 
more advanced in respect of their tissue. The hemapophysis is ossified like 
the so-called ‘abdominal ribs,’ and usually, like them, consists of two portions, 
having the special names of epihyal (39) and ceratohyal (40): the hemal 
spine (41) retains its cartilaginous state like its homotypes in the abdomen: 
there'they get the special name of ‘ linea alba’ or abdominal sternum, here 
of * basihyal.’ With respect to formal modification, this element is chiefly 
remarkable in the crocodile for its broad expanse: it sustains the ascending 
valvular ridge at the base of the tongue, which, applying itself against the 
descending ‘ palatum molle,’ constitutes an effectual barrier against the entry 
of water into the glottis from the mouth, whilst the crocodile is engaged in 
overcoming the struggles of a submerged and drowning prey. 
There being no need of diverging appendages from the hyoidean arch in 
‘the crocodile, brauchiostegal rays are not developed. The scapular arch is 
similarly simplified in Anguts and other serpentiform lizards ; but, to those 
who recognise its true homology, its presence without a trace of its appen- 
dages, the fore-limbs, will create no more surprise, than the presence of the 
hyoidean arch without the branchiostegal fins or of the mandibular arch without 
the opercular fins. 
On removing the neural arch of the parietal vertebra, with or without the 
section of the connate centrum (5), the bones completing, with the part (9), 
the corresponding arch of the frontal vertebra present the general arrange- 
ment shown in fig. 20.° 
The compressed produced 
bone, 9, shown in natural con- 
nection with the bone 10 in 
fig. 9, notwithstanding its mo- 
dified form, presents all the 
essential characters of the cen- 
trum of the arch: although it 
may have been developed ex- 
clusively from the capsule of 
the notochord, like the coa- 
leseed inferior parts of the cer- 
vical centrums in the silurus: 
there is no distinct ossicle an- 
swering to the central part of 
the centrum of the frontal ver- 
tebra, likeo', fig.5,in certain 
bony fishes. On the other hand, 
awefindthe neurapophysial cha- 
racters of the orbito-sphenoids 
(10, 10) more largely and typi- 
cally manifested in the croco- 
dile: they are smoothly excavated within by the sides of the prosencephalon : 
they dismiss the great special-sense nerves of the eye by the notch (fig. 9, op), 
and the motor nerves by the notch s: they show, however, the same ten- 
dency to change of position as the succeeding neurapophyses; for though 
Disarticulated prosencephalie arch, viewed from 
behind: Crocodile. 
_ they support a greater proportion of their proper spine (11), they also sup- 
port part of the succeeding spine (7), and rest below in part upon the pa- 
