ORIGIN OF JAW APPARATUS atl 
D. Muscles of the pharynx and gills 
IX............... 26. Constrictor pharyngis 
1D Fae ee re ee 27. Constrictor branchiarum et cardiae 
E. Muscles of the trunk 
Bpeljs.sl-...:..2 28: | Parietalis 
Spec doe wi eestes 29. Obliquus 
2) Deed oo eS Sea 30. Rectus 
F. Muscles of the cloacal region 
SDMA he deste Seales 31. Sphincter cloacae 
G] hoe GoORToe ene 32. Transversus caudalis 
Bile cn arcs, = 33. Cordis caudalis 
Fig. 27 Front view of the same dissection (37-mm. embryo), to show -rela- 
tion of the external tentacles to mouth and the cartilaginous skeleton of the jaw 
apparatus. 
This may be subject to some changes as a result of further 
study of the interrelations of the muscles and skeleton, partic- 
ularly after a study of their embryology and a more complete 
knowledge of their innervation which as published is both in- 
accurate and incomplete. 
The attachment of the mandibular mechanism to the base 
of the skull and its association with the maxillary mechanism 
is a remarkable work of codrdination and correlation which has 
taken place in the vertebrate stock above the Myxinoids. An 
interesting variety of experiments involving the use of numerous 
mechanical devices is presented by the cartilaginous fishes, 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 33, NO. 4 
