THE EVIDENCE OF THE SKELETON 123 
In addition, a branchial skeleton exists, which consists of a series 
of bars known as the branchial bars, so situated as to afford support 
to the successive branchial pouches, An anterior arch known as the 
mandibular arch (Fig. 50, 
Mn.), placed in front of the 
hyo-mandibular cleft, and 
a second arch, known as the 
hyoid arch (Hy.), placed in 
front of the hyo-branchial 
cleft, are developed in all 
types; the succeeding arches 
are known as the true bran- 
chial arches (Br.), and are 
only fully developed in the 
Ichthyopsida. In all cases 
of jaw-bearing (gnathosto- 
matous) vertebrates the first 
arch has become a support- 
a = ‘ Mn Hy Br, 
Hm Na Tr 
Fic. 50.—Hrap or EmBryo DoaG-FIsH, ELEVEN 
LINES LONG. (From PaRKER.) 
Cy" 
Tr., trabecula; Mn., mandibular cartilage; Hy., 
hyoid arch; Br,., first branchial arch; WNa., 
olfactory sac; H., eye; Au., auditory capsule ; 
Hm., hemisphere; C,, C,, C;, cerebral vesicles. 
ing skeleton for the mouth (Fig. 51), and in the higher vertebrates in 
combination with the second or hyoid arch takes part in the formation 
of the ear-bones. 
The true branchial arches persist, to a certain extent, in the 
Fie. 51.—Sxunt or Aputt Doc-risH, Sipz View. (From Parker.) 
cr., cranium; Br., branchial arches; Mn. + Hy., mandibular and hyoid arches. 
Amphibia, and become still more degenerated in the Amniota 
(reptiles, birds, and mammals) in correlation with the total dis- 
appearance of a branchial respiration at all periods of their life. 
