458 ZOOLOGY SECT. 



band of nerve-fibres, the united optic tracts, from the anterior border 

 of which the optic nerves are given off. Behind the tuber cinereum, 

 and formed as a thickening of its posterior wall, is a rounded eleva- 

 tion, the corpus mammillare (c. ma.). 



In the mid-brain the dorsal part is remarkable for the fact that 

 each optic lobe is divided into two by a transverse furrow, so that 

 two pairs of lobes (o.Z. 1 , o.l. 2 ), the corpora quadrigemina, are produced. 

 Between the anterior lobes passes the delicate posterior commissure 

 (p.co.). On the ventral region of the mid-brain the crura cerebri are 

 far more prominent than in the lower groups. In the hind-brain 

 the cerebellum (Fig. 1105, cb'^cb".) is very large ; it consists of a 

 central lobe or vermis and two lateral lobes, divided by very numerous 

 fissures or sulci into a large number of small convolutions. Each 

 lateral lobe bears an irregularly-shaped prominence, the flocculus. 

 On section (Fig. 1107, cb.) the cerebellum exhibits a tree-like pattern 

 (arbor vitce) 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 transverse band, the valve of Vieussens (Fig. 1107, v. vn.), 

 connected by its anterior edge with the corpora quadrigemina. 

 Behind this is a short tract of transverse fibres the corpus 

 trapezoideum 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 coeliac 

 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 



