376 HOWARD AYERS 
on the cartilages of the hyoidean apparatus and the cranial 
skeleton which has also developed a number of new cartilages 
and increased the relative size and strength of its tendon and 
fibrous bands. The muscles of Bdellostoma may be grouped 
according to derivation as follows: 
Group 1. Muscles of the jaw apparatus. The most ancient muscles of the 
vertebrate head, not considering the but little differentiated myotomes. The 
muscles of this group are all derived from the ventral transverse muscle of Am- 
phioxus. Some of them have already acquired a longitudinal direction in Am- 
phioxus. This process is continued in Ammocoetes and Bdellostoma. 
A. Muscles of the jaw bars 
a. Of the dentigerous jaw: 
Retractors 
INGE ees tyes 1. Mandibularis (longitudinalis linguae) 
11, (Cs Revel Ra a 2. Perpendicularis 
Protractors 
3. Hyo-copulo-glossus 
4. Copulo-glossus superficialis 
5. Copulo-glossus profundus 
b. Of the distal part of the jaw bar and tentacles: 
QipGh. atone ae 6. Nasalis 
Opthi:aseseeece 7. Tentaculo-posterior 
Onthieseceesc nas 8. Tentaculo-ethmoidalis 
Opthos eendsioes 9. Transversus oris 
Optlissse.ecase ke 10. Ethmoideo-nasalis 
Optics ae 11. Palato-ethmoideo-superficialis 
INES aterm eetne Meet 12. Palato-ethmoideo-profundus 
B. Muscles of the hyoidean apparatus 
U5 ote ae eae 13. Palato-coronarius 
IM eaxetarr aster cay sare 14. Copulo-tentaculo-coronarius 
IMeixatat spans ots oer 15. Coronarius 
Tea sresek <2) acy cts es 16. Copulo-ethmoidalis 
IW ilifears 5 keep 17. Copulo-copularis 
Max (VII?)...... 18. Copulo-palatinus 
EDT et ees 19. Hyo-copulo-palatinus 
VIL......... 20. Copulo-quadratus superficialis 
VIL......... 21. Copulo-quadratus profundus 
VII......... 22. Cranio-hyoidens 
WEES a ths 58 Medora ce 23. Quadrato-palatinus 
C. Muscles of the velum 
Md.............. 24. Velo-quadratus 
Md?....3<......0. 25: ‘Velo-spimalis 
