472 ZOOLOGY SECT. 



consists of a central lobe or vermis and two lateral lobes, divided by 

 very numerous fissures or sulci into a large number of small con- 

 volutions. Each lateral lobe bears an irrregularly shaped promi- 

 nence, the flocculus. On section (Fig. 1096, c6.), the cerebellum 

 exhibits a tree-like pattern (arbor mice) brought about by the 

 arrangement of the white and grey matter. On the ventral aspect 

 of the hind-brain a flat band of transverse fibres the pons Varolii 

 connects together the lateral parts of the cerebellum. The 

 cerebellum is attached to the other parts of the brain by three 

 pairs of peduncles, the anterior, connecting it with the posterior 

 optic lobes, the middle, passing on each side into the pons Varolii, 

 and the posterior, connecting it with the dorsal portion of the 

 medulla oblongata. Between the anterior peduncles extends a 

 tranverse band, the valve of Vieussens (Fig. 1096, v. vn.\ con- 

 nected by its anterior edge with the corpora quadrigemina. 

 Behind this is a short tract of transverse fibres the corpus 

 trapezcideum and behind this again is a slightly elevated area 

 marking the position of the olivary body. The floor of the 

 fourth ventricle presents a median groove which ends posteriorly 

 in a pointed depression calamus scriptorius leading into the 

 central canal of the spinal cord. 



The Rabbit, like most other Vertebrates, possesses a sympathetic 

 nervous system, consisting of a series of ganglia united together by 

 commissural nerves, and giving off branches to the various internal 

 organs. Two sympathetic ganglia are situated on each side in the 

 neck the anterior and posterior cervical ganglia. From the anterior, 

 nerve-branches pass forwards to enter the cranial cavity ; from the 

 posterior a nerve-cord passes backwards to the first thoracic 

 ganglion. Of the thoracic ganglia there are twelve on each side. 

 From one of the more posterior of these originates the splanchnic 

 nerve which passes backwards into the abdomen, ending in a 

 ganglion -the cceliac connected with an extensive nerve-plexus, 

 the ccelaic plexus, In the abdomen there are, on each side, 

 twelve ganglia, the chain ending behind in a single ganglion 

 impar. 



In the organs of special sense the following special features 

 are to be seen when a comparison is made with the Pigeon or 

 Lizard. In the eye, the sclerotic is composed entirely of dense 

 fibrous tissue ; the pecten is absent. In the internal ear the 

 principal point of difference is in the special development of the 

 cochlea. This part of the membranous labyrinth, instead of 

 retaining the simple curved form which it presents in the Bird, 

 is coiled on itself in a close spiral of two-and-a-half turns. The 

 spiral channel in the substance of the bone, in which this cochlear 

 spiral runs, contains three passages ; the middle one, much the 

 smallest, being the membranous cochlea, the uppermost the scala 

 vestibuli, and the lowermost the scala tympani. 



