VISCERAL CLEFTS AND VISCERAL ARCHES. 35 
and a portion of the helix of the pinna of the external ear are formed. The carti- 
laginous bar in its interior is known as Meckel’s cartilage. It forms the primitive 
skeleton of the arch. Its upper and lower extremities are ossified and remain in 
the adult, the former as the malleus, and possibly the incus, and the latter as the 
symphysial part of the lower jaw. The remainder of the cartilaginous bar dis- 
appears, but the fibrous membrane which surrounds the lower section of the inter- 
mediate part is ossified and converted into the main part of the lower jaw, whilst 
that round the upper section of the intermediate portion persists as the spheno- 
mandibular ligament. The blood vessel developed in the mandibular arch is, for 
the main part, a transitory structure, but its ventral section is converted into the 
internal maxillary, superficial temporal, and lingual arteries. 
The second and third arches are continued downwards into the floor of 
the pharyngeal 
portion of the 
fore-gut. There, 
converging, they 
insinuate them- 
selves between 
the tuberculum 
impar and_ the 
furcula, across 
the anterior part 
of the sinus 
arcuatus, and 
uniting together 
form atransverse 
bar. This rapidly 
changes into a T 
semilunar ridge, i 
which embraces \ 
the posterior part 
of the tuber- 
culum impar, 
with which it 
fuses,anditforms 
the posterior 
third of the Fic. 28.—Sraces iy THE FoRMATION OF THE TONGUE AND Upper APERTURE OF THE 
tongue. LARYNX IN THE HuMAN EmpBryo (after His). 
The second I. Embryo 14 days old. II. Embryo 23 days old. III. Embryo 28 to 30 days old. 
IV, Embryo 2 months old. 
<n és 2 
Ky es 8 / 3 
Ill 
arch takes part 
. . 1 Y int gl 1 air 
in the formation Be C. Coelom. — G. Glottis. 
Pnaeside and 3 Visceral E. Epiglottis. SA. Sinus arcuatus. 
: * [ arches. F. Furcula. T. Tongue. 
anterior part of Z FC. Foramen cecum. TI. Tubereulum impar. 
P 5 p 
the neck. From 
its anterior border externally a part of the helix, the antihelix, the antitragus, 
and the lobule of the pinna of the external ear are developed. The lower and 
upper portions of its cartilaginous bar—the hyoid bar—are ossified; the lower 
portion forms part of the body and the small cornu of the hyoid bone on its 
own side, and the upper portion is converted into the intra- and extra-temporal 
sections of the styloid process (the tympano-hyal and stylo-hyal portions of the 
styloid process of the temporal bone). The fibrous tissue of the intermediate part 
of the hyoidean bar persists in the adult as the stylo-hyoid ligament. The blood- 
vessel of the hyoid arch, the second cephalic aortic arch, almost entirely disappears, 
but from its ventral extremity the ascending pharyngeal, occipital and posterior 
auricular arteries are probably developed. 
The third visceral arch forms part of the neck posterior to the region of the 
second arch, and, as already pointed out, its lower end takes part in the formation 
of the posterior part of the tongue. The upper and middle parts of its cartilaginous 
bar disappear, but the lower part persists and is converted into the posterior part 
