Bawden, Nose and Jacobsoiis Organ. 125 



semi-aquatic animals which frequent the water most that the 

 hippocampus and radices are correspondingly reduced. The 

 whole region in the limbic lobe below the rhinalic fissure is 

 given up to the somatic senses in general, and to smell more 

 especially. 



The olfactory fibres probably do not develop from the ol- 

 factory lobe, but rather take their origin from the epithelium of 

 the olfactory pits. It is likely that they originate primarily 

 from the cells of the spinal ganglion as they bud out from the 

 region of the neuro-pore. All evidence goes to show that they 

 grow in from without rather than in the opposite manner. In 

 the earliest stages the olfactory pits have no nerves. Later 

 there is noticed a slight proliferation in the direction of the 

 nerve tube. And it is just at this point that lack of decisive 

 evidence makes it uncertain whether the olfactory nerve derives 

 its fibres from the olfactory ganglion only or whether there is an 

 interaction, fibres also growing out from the tuber. The former 

 seems most likely. The tuber at its cephalic extremity, i. e. 

 the bulb, in general, consists of two well-defined portions called 

 the pero, the thick, outer, fibrous, buskin-shaped layer, and the 

 pes, the inner, cellular layer. The pero is formed by the fibres 

 of the olfactory nerve which diverge over the surface interlacing 

 and commingling, thus forming the above-mentioned sheath-like 

 cap enveloping the pes. The pes may be called the cerebral 

 part of the bulb since no fibres pass from it without into con- 

 nection with the olfactory epithelium. The adhesion of the 

 pero to the pes is apparently of a secondary character, being 

 probably mechanical, without any morphological connection. 

 The internal structure of the pero would seem to show the 

 same. The fact that the fibres lose their sheaths in their pas- 

 sage through the pero, but acquire them at their exit, would 

 also attest it. {Journ. Covip. Neurol., Vol. II, Feb., '92, 

 pp. 2-7.) 



The inner structure of the olfactory bulb may here be noted 

 briefly. Passing entad we encounter successively the following 

 layers: first, the fibrous outer layer consisting of apparently ir- 

 regularly disposed fibre clusters, intercrossing confusedly, (i. e. , 



