OSSEOUS SYSTEM. (Comp. Anat.) 
The styloid bones(29), mererudiments ' 
in the human skeleton, anchylosed with 
the rest of the temporal bone, of which 
they are called the “ styloid process,” 
in the water-breathing Vertebrata are 
distinct pieces interposed between the os 
hyoides and the base of the skull, serving 
to unite the former to the latter. 
The symplectic bones (31) seem to be 
peculiar to Fishes ; they accompany the 
transverse, and assist in connecting the 
articulation of the lower jaw with the 
te latine apparatus. 
F The lawer jaw, Ephotsh in the adult 
human subject formed of a single piece, | 
in the /etus consists of two lateral halves 
united by a symphysis, as it is perma- 
nently in many of the lower Quadru- 
peds. In Reptiles and Fishes, how- 
ever, each half consists of numerous 
jieces, to which distinct names have 
m given by the comparative anato- 
mist. In the Crocodile and most reptiles 
there are six in number, viz. the dental 
portion (34), in which are situated all 
the alveoli of the teeth, uniting with its 
fellow to form the symphysis of the jaw- 
The opercular, covering almost all the inner 
aspect of the jaw except in front. 
The angular (36) and the supra-angular (35), 
placed one above the other, reaching quite to 
the posterior extremity of the jaw. In the 
Crocodile they leave between them a conside- 
rable space occupied anteriorly by the end of 
the dental portion, and then by a large oval 
aperture. 
The urticular (e), bearing the articular pro- 
cess, whereby the jaw is connected with the 
skull. Likewise another small and unimpor- 
tant plate of bone sometimes seen on the inver 
aspect of the inferior maxilla. 
In the Chondropterygious Fishes the lower 
jaw is made up of only one bone, the arti- 
ar, upon which the teeth are affixed: rudi- 
Fig. 446. 
Human Shull. 
833 
Fig. 445. 
Padi Un 
Human Shull. 
ments of the others are, however, met with 
imbedded in the flesh beneath the skin. 
The hyo-branchial apparatus—The osseous 
framework to which in the human subject the 
name of os hyotdes has been appropriated, from 
the trivial circumstance that in the simple con- 
dition under which it presents itself in man 
it resembles the Greek letter v, is found in the 
lower Vertebrata to be permanently composed 
of very numerous pieces, which are made sub- 
servient to respiration, and from their size and 
number render the whole apparatus, which 
they assist in forming, really worthy of the 
name of an anterior thorax. The hyoid system 
of bones may indeed be regarded as being in 
some respects vicarious in function with the 
true thorax, the former belonging especially to 
the aquatic, the other to the aerial mode of 
respiration ; whilst, therefore, as 
in Fishes, the gills form the only 
meansof breathing, andthe branchial 
arches exist in their full state of 
developement, the hyo-branchialap- 
paratus is complete and preponde- 
rates in importance over the thorax ; 
but, in proportion as pulmonary 
respiration is established, as we 
ascend the scale of animal existence, 
the thoracic system of bones as- 
sumes the principal duties con- 
‘ nected with the inspiration and 
expiration of air, and the os hyoides - 
dwindles into a very rudimentary 
condition. The above circum- 
stances however, interesting as they 
are when a mere comparison is 
instituted between the hyoid bones 
of various animals as to their com- 
position when in the adult state, 
assume additional importance when 
we reflect that all the higher Ver- 
tebrata possess in the earlier stages 
3H 
