276 NERVE COMPONENTS OF BONY FISHES. 



I. — The presence in the spinal cord of two motor nuclei, 

 the ventral horn and the paracentral nucleus. The for- 

 mer is a somatic centre and is probably represented in 

 the head by the eye-muscle nerves only; the latter is 

 probably a visceral centre, represented in the head by the 

 viscero-motor nuclei, viz., the motor X, IX, VII and V. 

 See Section 3, III and IV. 



2. — The first spinal is a fusion of two segmental nerves. 

 The more cephalic one (occipito-spinal nerve b of Fiir- 

 bringer) contributes a part to the brachial plexus, the 

 remainder supplies the post-hyal hypoglossus musculature. 

 The pre-hyal hypoglossus musculature is wanting in the 

 teleosts and, in correlation with this, the spino-occipital 

 nerve a of most other vertebrates is reduced. See Section 

 4, V. 



3. — The post-hyal ventral musculature is innervated by 

 the first spinal nerve, as usual. The pre-hyal hypo- 

 glossus musculature is functionally replaced in the 

 teleosts by a derivative of the constrictor system of the 

 trigeminal segment of the selachians, viz., the so-called 

 m. genio-hyoideus and the intermandibularis. These 

 muscles in Menidia are innervated from the motor V (not 

 motor VII, as commonly described), and can have nothing 

 to do with the true ventral musculature. The first spinal 

 nerve suffers a corresponding reduction. See Section 7, 

 IV, 5, iv. 



4. — The pharyngo-clavicularis muscles are innervated 

 from the vagus and not from the first spinal. This differs 

 from the accounts of some others, especially Fiirbringer, 

 and will necessitate some modifications in that author's 

 scheme of the relations of somatic and visceral muscles in 

 the vagus region of teleosts. See Section 5, VII, 5, v. 



