294 



THE ORIGIN OF VERTEBRATES 



(,s7t4, shs), by tlie section of the separate branchiae (&r 2 , br 3 ), and by the 

 separate segmental muscles arranged round each bar, these muscles 

 being partly ordinary striated (m 4 , w 5 ), partly tubular (mt s , rati). The 

 uppermost of these branchial segments shows the same arrangement ; 

 (.s7,' 3 ) is the branchial skeletal bar, which is now composed of niuco- 

 cartilage, not cartilage ; (h\) is the branchiae 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 (?%), being separated from the tubular muscles of 

 the segment (m£ 2 ) 3 owing to the large size of the blood-space in which 



aud 



mL eye 



mti 



Fig. 117. — Sagittal Lateral Section through the Anterior Part op Ammocctites. 

 Lettering and colouring same as in Fig. 116. and., 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 (s7c 2 ) of muco- cartilage, 

 evidently indicating a similar segment anterior to the hyoid segment. 

 In connection with this bar there are no branchiee, but a^ain we see 

 two sets of visceral muscles, the one ordinary striated, marked (m 2 ), 

 and the other tubular, marked (mti). 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 



