218 NERVOUS SYSTEM. 



in a thick cartilaginous cranium, which is perforated for 

 the passage of nerves, and gives attachment externally to 

 the muscles of the head and trunk. The cranium is 

 continued round the oesophagus though soft on its 

 interior part. Immediately anterior to the brain and the 

 cranium is a large heart-shaped supra-cesophageal ganglion, 

 of a yellowish colour, resting over the oesophagus, and 

 sending forwards numerous large nerves to the labial ap- 

 paratus enveloping the mandibles. On the lower part of 

 the muscular bulb of the mouth, are two small lateral 

 ganglia, which send in numerous large branches to the 

 strong muscles of the mandibles. Both the labial and 

 the mandibular ganglia are connected with the brain by 

 distinct nervous chords. Below the ossophagus, and an- 

 terior to the cranium, are two large lateral pedal ganglia, 

 which send forwards large nervous trunks to pass ramify- 

 ing through the tubular axis of all the feet. These two pedal 

 ganglia are likewise connected by nervous chords with 

 the sides of the brain. The two optic nerves pass through 

 the cranium, from the superior or dorsal lobes of the 

 brain, and enter two large crescentic optic ganglia within 

 the sclerotic, as in other naked cephalopods. The two 

 great longitudinal nervous columns are extended backwards 

 from the sides of the brain, separate from each other, and 

 along the dorsal aspect of the trunk, above the abdominal 

 cavity to the large palleal ganglia which distribute radiating 

 nervous chords chiefly to the interior muscular parts of the 

 mantle. The inner portion of each of these two symmetrical 

 columns (Fig. 93. A. b. d.) extending from the brain, along 

 the dorsal region of the cephalopods, does not enter the 

 palleal ganglion, but passing along the inner margin of 

 that ganglion, it penetrates the substance of the mantle 

 by a distinct foramen, and radiates into numerous rami- 

 fying chords, which are distributed chiefly on the exterior 

 parts of the trunk. The principal branches of these ex- 

 terior palleal nerves extend backwards in the direction of 

 the broad thin cartilaginous laminee which support the 

 branchial muscles, and two filaments extend inwards to 

 the abdominal sympathetic ganglia (93. A. e. e.) placed at 

 the base of the branchiae, near the lateral hearts. By means 

 of the two sub-cesophageal pedal ganglia anterior to the 



