294 THE ORIGIN OF VERTEBRATES 
(sks, sks), by the section of the separate branchiv (79, 073), and by the 
separate segmental muscles arranged round each bar, these muscles 
being partly ordinary striated (24, ms), partly tubular (mts, mt,). The 
uppermost of these branchial segments shows the same arrangement ; 
(skg) is the branchial skeletal bar, which is now composed of muco- 
cartilage, not cartilage ; (b7;) is the branchie in the same situation as 
the others, but here composed of glandular rather than of respiratory 
epithelium, while the ordinary striated branchial muscles of this seg- 
ment are marked as (ms), being separated from the tubular muscles of 
the segment (mp), owing to the large size of the blood-space in which 
aud mt, we 
™4 sk i oat 
Mt 
Sky 3 Tsk 
Fic. 117.—SacittaL LATERAL SECTION THROUGH THE ANTERIOR Part OF AMMOCGTES. 
Lettering and colouring same as in Fig.116. awd., auditory capsule; j.v., jugular vein. 
these latter muscles are lying. In front of this segment so defined 
we see again another well-marked skeletal bar (sk) of muco-cartilage, 
evidently indicating a similar segment anterior to the hyoid segment. 
In connection with this bar there are no branchie, but again we see 
two sets of visceral muscles, the one ordinary striated, marked (me), 
and the other tubular, marked (mt,). Here, then, the section indicates 
the existence of a segment of the same character as the posteriorly 
situated branchial segments but belonging to a non-branchial region 
—a segment which would represent a non-branchial appendage, the 
last, therefore, of the prosomatic appendages. Let us, then, follow 
