1050 DISSECTION OF THE HEAD AND NECK. 



the corpus callosum near the forepart, and raising it carefully, divide with 

 scissors the septum lucidum which separates the lateral ventricles, and 

 notice between its layers the fifth ventricle. The lateral ventricles having 

 been thus thrown into one, the structures forming their floor are more fully 

 seen, viz., the corpora striata, teeniaa semicirculares, the optic thalami iu 

 part, the choroid plexus, the upper surface of the fornix, the foramen of 

 Monro, the anterior and posterior cornua, and the hippocampus minor. 

 The descending cornu is now to be exposed, on one side only, by cutting 

 away the cerebral substance above and external to it, and in it will be 

 found the hippocampus major, pes hippocampi, tseiiia hippocampi, and fascia 

 dentata. 



The fornix is to be divided immediately above the foramen of Monro, 

 and reflected ; by which means its inferior surface will be brought into 

 view, as also the upper surface of the velum interpositum. The connections 

 of the anterior extremity of the velum may then be cut across, and that 

 structure likewise turned back so as to lay bare the third ventricle ; but iu 

 doing this care should be taken lest the pineal body, which is adherent to 

 the under surface of the velum interpositum near its back part, should bo 

 raised out of its place. The objects seen in and near the third ventricle, 

 are now to be studied : viz., the optic thalami, the three smaller commis- 

 sures, viz., anterior, middle and posterior, the pineal body and its crura, 

 the corpora quadrigemiua, and the anterior opening of the iter a tertio ad 

 quartum ventriculum ; also the anterior crura of the fornix should be traced 

 down as far as possible towards the corpora albicantia. The velum having 

 been replaced, the transverse fissure of the cerebrum ought now to be 

 opened by division of the remains of the corpus callosum and fornix in the 

 middle line, and it may be followed in its whole extent to the extremity of 

 the descending cornu. By this proceeding the veins of Galen will be traced 

 back through the velum interpositum to the margin of the tentorium, and, 

 on division of the velum, the valve of Vieussens and the origin of the fourth 

 nerve, as well as that of the optic tract, may be seen ; but if the view of 

 these objects should not be satisfactory, they may be again examined after 

 removal of the brain from the skull. 



The remaining part of the brain is to be removed by cutting the teuto- 

 rium on each side sufficiently to allow the cerebellum to be raised, and 

 dividing the spinal cord and vertebral arteries as low as possible, the spinal 

 accessory and suboccipital nerves, and the cranial nerves in order from be- 

 hind forward, with the infundibulum and internal carotid arteries ; after 

 which the brain is to be laid on a flat plate with the base uppermost. If, 

 however, it has been decided to remove the brain entire from the body, this 

 may either be done in the manner now described, or, with the subject 

 temporarily placed for the purpose on its back. According to the latter 

 mode of procedure, which is the most customary, the anterior lobes of the 

 brain are gently raised, and the olfactory bulbs lifted from the surface of 

 the ethmoid bone ; the optic nerves, internal carotid arteries, the infundi- 

 bulum, and the third pair of nerves are successively divided ; the anterior 

 attachment of the tentorium is then to be cut on each side so as to secure 

 the divisions of the fourth pair of nerves before they have any chance of 

 being torn. The tentorium is then to be more extensively divided, and 

 after it, in their order, the remaining nerves, the vertebral arteries, and the 

 spinal cord. In studying the base of the brain, the distribution of the 

 arteries should be first observed, with their union in the circle of Willis 

 (p. 363). After they are removed, and the less adherent portions of the 



