14 



one large central lobe, marked out into a series of transverse lamellae by 

 fissures or involutions ; to either side of it small lateral lobes are appended, 

 and in section it presents a distinct Arbor vita. No pons varolii seems 

 to exist even in rudiment. The carotid arteries ramify on the surface 

 of the organ, and the vertebrals pass on the side of the medulla oblon- 

 gata. From the base of the brain pass the cerebral nerves. The first, or 

 olfactory, runs to the nose, under a bony shelf, from the anterior and 

 inferior portion of the cerebrum, where a small conical eminence is 

 observable ; it is extremely soft and somewhat greyish at its origin. The 

 second, or optic, arises from the optic lobes, curves downwards and for- 

 wards, and meets in front of the infundibular fold of pia mater with 

 its fellow of the opposite side ; the decussating fibres are easily seen at 

 the commissure. The third and fourth nerves pass to the orbit, where 

 they supply the muscles; they arise between the medulla oblongata and 

 the posterior cerebral tubercles. The trifacial nerve is very small, and 

 has an extremely small supra-orbital branch. The eighth pair sends off 

 a large glosso-pharyngeal to the tongue, along with a glossal branch of 

 the pneumogastric. None of the other nerves display any points of 

 interest. 



On removing the upper part of one of the cerebral hemispheres, the 

 large lateral ventricle is exhibited, closed internally from the median 

 fissure by a thin p]ate, white on the ventricular, and grey on the inter- 

 nal aspect. This plate is connected with the opposite side by a narrow 

 white band, easily torn, and situated far back, not far from the posterior 

 cerebral tubercles ; this seems to be similar to the band described by A. 

 Miiller as a rudimental corpus callosum. Each lateral ventricle consists 

 of one part, and presents no cornua ; it has two large grey masses on its 

 floor — one large, anterior, the corpus striatum; another smaller, posterior, 

 the optic thalamus, separated by a rudimentary taenia ; overlapping the 

 thalamus is a large fold of pia mater, which gains entrance posteriorly ; 

 this is the choroid plexus. 



Posterior to the cerebral hemispheres appear the optic lobes or tuber- 

 cles, which are covered by a layer of pia mater, enclosing a small oval 

 pineal gland ; these tubercles are hollow, and their cavities communicate 

 with the lateral ventricles ; in front of them passes a posterior commis- 

 sure, which overlaps a large iter ad quartum ventriculum, or Sylvian 

 aqueduct. The fourth ventricle is placed anterior and inferior to the 

 cerebellum, and presents a very well marked calamus scriptorius. The 

 spinal cord is fissured deeply in front and behind, and is enveloped in 

 three membranes ; each spinal nerve arises by two roots, of which the 

 anterior is much the smaller ; these pass separately through the dura 

 mater, and unite outside the foramina of conjugation of the vertebrae, the 

 posterior forming a ganglion which the anterior crosses, and the two 

 roots are united immediately external ; a branch of the sympathetic can 

 be traced to each ganglion. The roots of the spinal nerves are not sepa- 

 rated by a ligamentum denticulatum, but pass obliquely downward and 

 outward, converging. The sympathetic is a small cord, passing along 

 the spine, behind the aorta, and forming a solar plexus around the 

 coeliac axis. 



