Herrick, Morphology of Brain of Bony Fishes. 217 



opercular region. Arising from the ganglion of the vagus 

 immediately dorsad of the l^tst is a very small fibre passing 

 to the lower pharyngeal region. Farther dorsad is the visceral 

 branch of the vagus. This gives a small branch to the 

 middle of the fourth gill and a larger one to the organs of the 

 thorax. The main trunk passes caudad and spreads out over 

 the stomach, mesentary, etc. The largest division of the 

 vagus nerve is the nerve of the lateral line. It communicates 

 by a delicate plexus with the nerves of the muscles of the 

 pectoral fin and the cutaneous nerve connected with them, 

 then passes caudad superficially along the lateral line for the 

 whole length of the body. The spinal accessory nerve cannot 

 be separately distinguished. The first spinal nerve, which 

 might, perhaps, with equal propriety be called the twelfth 

 cranial nerve, arises behind the medulla by two roots, dorsal 

 and ventral. The latter is considerably farther cephalad 

 than the former. The two roots remain distinct until after 

 they pass through their foramen (Plate XVII, Fig. 5, n. s.p). 

 Rhinencephalon . — The olfactory lobes in the adult are in 

 immediate proximity to the nasal cavities, and therefore far 

 distant from the rest of the brain. In large specimens the 

 olfactory crura would thus be more than fifteen centimetres 

 long, while the olfactory nerves would be only a few mill- 

 metres. In very young specimens one inch long the brain is 

 so large that it fills the whole front part of the head, and the 

 olfactory lobes are in their usual position, closely appressed 

 to the cerebrum. Compare Plate XVII, Fig. 2, with Fig. 3. 

 Each lobe is sub-spherical, three millimetres in diameter, 

 attached to the cms on the caudal aspect, with the fibres of 

 the olfactory nerve springing from the opposite side. The 

 internal structure is very much as in reptilia. Ectad there 

 is a glomerulary zone which is well developed, though not 

 so much as in Hyodon. Within this are specific olfactory 

 cells irregularly and sparsely distributed in a single series. 

 They are fusiform to flask-shaped, with the apices usually 

 directed peripherally. The centre of the lobe contains small 



