NERVOUS SYSTEM. 647 



In the mammalian tarsus there are two rows of bones, and a central 

 bone interposed between the two rows on the inner or tibial side. 



In the rabbit the first tarsal and the corresponding toe or hallux are 

 wanting. There are thus only four metatarsals and digits. Each digit 

 has three phalanges, and ends in a claw. 



Nervous system. — The brain has the usual five parts— 

 cerebral hemispheres, optic thalami, optic lobes, cerebellum, 

 and medulla oblongata, but the cerebral hemispheres cover 

 the next two parts, and the cerebellum conceals the medulla. 

 Of the brain membranes, the dura mater lines the cranial 

 cavity, projecting longitudinally between the cerebral hemi- 

 spheres, and transversely between the latter and the cere- 

 bellum, while the vascular pia mater invests the brain 

 closely. There are the usual twelve pairs of cranial nerves. 

 The spinal cord gives off the usual spinal nerves, and there 

 is a sympathetic system as in most other Vertebrates. 



The cerebral hemispheres of the rabbit are very slightly convoluted, 

 and they leave the cerebellum quite uncovered. They are connected 

 transversely by a broad bridge — the corpus callosum, and beneath this 

 there is a longitudinal band of fibres — the fornix. The corpus callosum 

 is readily disclosed by gently separating the hemispheres. The outer 

 wall and floor of the anterior part of the cavity or ventricle of each 

 hemisphere is formed by a thick mass, called the corpus striatum, and 

 the internal cavity is lessened by a prominent convex ridge, called the 

 hippocampus major. The ventricles of the cerebrum communicate 

 with the third ventricle, between the optic thalami, by a small aperture, 

 called the foramen of Monro. In front of the hemispheres two club- 

 shaped olfactory lobes project. The thin cortical layer of the cerebrum 

 consists of grey (ganglionic) matter, and so does the thick corpus striatum, 

 while the central part consists of white matter (nerve fibres). 



The thalamencephalon is entirely hidden, but gives origin as usual to 

 the dorsal epiphysis, ending in a pineal body, which lies on the surface 

 between the cerebrum and cerebellum, and to the ventral infundibulum, 

 at the end of which the pituitary body lies, lodged in a fossa of the basi- 

 sphenoid. Immediately in front of the infundibulum the optic nerves 

 cross in a chiasma, from which optic tracts can be traced to the optic 

 lobes. Immediately behind the infundibulum lies a rounded elevation, 

 called the mammillary body. Anteriorly, on the ventral surface of each 



