396 HOWARD AYERS 
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Fig. 36 Composite picture to illustrate the amphioxine condition of the in- 
nervation of the jaw apparatus of Bdellostoma. The nerves are sketched in over 
a dotted outline of the major part of the head skeleton. These fundamental’ 
facts are illustrated: 1) The position of the buccal cavity (oral hood cavity) 
between the buccal aperture and the velum. The innervation of the latter. 
2) The persistence of an extensive amphioxine jaw apparatus composed of jaw 
bars with the proximal dentigerous jaws disconnected for free action, and ten- 
tacle bearing distal sections of the bars framing in the buccal aperture as in 
Amphioxus. 3) The plexiform innervation of the tentacular portion of the jaw 
apparatus forming the snout. 4) The enormously developed hyoidean jaw sup- 
ORIGIN OF JAW APPARATUS 397 
port. 5) The course of the five nerves controlling the jaw apparatus, forward 
and ventrad, carrying motor and sensory fibers for the innervation of jaw ap- 
paratus and its enclosed buccal cavity. 6) The branches of the nasalis innervat- 
ing the olfactory mucosa together with other features of innervation acquired 
since passing the Amphioxus stage, such as the lateralis nerves. 7) The caudad 
displacement of the velar folds with the muscles which operate the velum re- 
maining in their original territory near the mandibular nerve trunk. 
The significance of the numbers is as follows: 1, terminal nasal cartilage; 
2, olfactory lobe; 3, forebrain; 4, midbrain; 4, cerebellum; 6, medulla; 7, spinal 
cord; 8, first spinal nerve; 9, eye; 10, olfactory branches of nasalis nerve. 
