ORIGIN OF JAW APPARATUS 367 
tral line; the only indication of a median raphé is the interdigita- 
tion of some of the muscles, those not interdigitating have their 
fibers continuous. In front of the nasal capsule the dorsal 
B ZEN 
= yy 3 
Fig. 19 Dorsal view of the floor of the buccal cavity, velar chamber, and 
anterior end of branchial cavity of Ammocoetes. The right and left arms of the 
jaw bar are shown to the left and right of the median tentacle, also its median 
tendon extending caudad in the ridge in which the opening of the thyroid gland 
occurs. The velum with the ventral attachment of its muscle and the positipn 
of the anterior gills are also shown. 
layer runs into the upper lip and the bundles cross each other. 
Below the capsule two heavy bundles arising from the lateral 
surface of the ring muscle next the mucosa run into the upper 
lip, crossing one another in front of the palatine loop. In the 
