xiii PHYLUM CHORDATA 443 



lateral parts of the cerebellum. The cerebellum is connected with 

 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, the posterior, connecting- 

 it with the dorsal portion of the medulla oblongata. Between 

 the anterior peduncles extends a transverse band, the valve of 

 Vieussens (Fig. 1033, v. vn.), connected by its anterior edge with 

 the corpora quadrigemina. Behind this is a short tract of trans- 

 verse fibres the corpus trapezoideum and behind this again is 

 a slightly elevated area marking the position of the olivary bod//. 

 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 cranial nerves are similar to those of the Pigeon in most 

 respects, differing in some of the particulars of their arrangement 

 and distribution. 



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 codiac. 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 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 vcstibuli, and the 

 lowermost the scala tympani. 



The special features of the middle ear with its auditory ossicles 

 have been already referred to. 



Urinogenital Organs. --The kidneys are of somewhat com- 

 pressed oval shape, with a notch or hikes on the inner side. They 

 are in close contact with the dorsal wall of the abdominal cavity, 

 the right being somewhat in advance of the left. Towards the 



