CRANIOCEREBRAL TOPOGRAPHY. 35 



vertebral canal through the intervertebral foramina, meningeal branches to the dura mater in the 

 posterior cerebral fossa, and the anterior and posterior spinal branches to the spinal cord and its 

 membranes. 



The internal carotid artery supplies the brain with: 



1. The anterior cerebral artery. It passes inward over the dorsal surface of the corresponding 

 optic nerve and then forward, approaching the artery of the opposite side, with which it is con- 

 nected by the anterior communicating artery. The vessels winding around the genu of the corpus 

 callosum pass backward, supplying the corpus callosum, and ramify upon the median surface 

 of the cerebral hemispheres. 



2. The middle cerebral artery, which runs in the fissure of Sylvius, supplying the frontal, 

 parietal, and temporal lobes as well as the island of Reil. 



3. The anterior choroid artery, passing posteriorly along the optic tract to the descending 

 horn of the lateral ventricle to enter the choroid plexus. 



4. The posterior communicating artery, which has been previously mentioned. 



CRANIOCEREBRAL TOPOGRAPHY. 



The tentorium cerebelli (see Figs. 2, 9, 17, and Plate 4) divides the cranial cavity into two 

 closed spaces which communicate with each other through the incisura tentorii. The larger 

 anterior space includes the anterior and middle cranial fossas and lodges the cerebrum; the 

 small posterior space the posterior cranial fossa contains the cerebellum, the pons, and the 

 medulla. A frontal section through the back part of the head, posterior to the incisura tentorii 

 (see Fig. 12), reveals four separate compartments having apparently no connection with each 

 other, since the falx cerebri, the falx cerebelli, and the tentorium form a cross-like partition 

 which separates the hemispheres of the cerebrum and cerebellum. The plane of such a cross- 

 section will be better understood after a study of other illustrations (Fig. 9, Plate 4). The 

 following relations will be made more clear to the mind of the reader by looking at the base of 

 a skull (see Fig. 9 and Plate i). 



The anterior cranial fossa lodges the frontal lobes of the cerebrum ; the marked develop- 

 ment of the juga (ridges) cerebralia and of the impressiones digitatae on the thin orbital plate of 

 the frontal bone are due to the orbital sulci and gyri respectively. In the median line the 

 olfactory bulb rests upon the cribriform plate of the ethmoid and gives off the olfactory filaments 

 to the nasal cavity. 



The middle cranial fossa contains the temporal lobes. Its posterior and lateral portion bears 

 an important relation to the roof of the middle ear (tegmen tympani). This is the situation at 

 which abscesses develop in the temporal lobes as the result of suppurations in the middle ear. 

 Another important situation in the middle cranial fossa is located anteriorly near the median line, 

 where the large semilunar ganglion is found with its three main divisions (see page 32). The pos- 

 terior border of the lesser wing of the sphenoid corresponds to the deep fissure of Sylvius situated 

 between the frontal and temporal lobes. The optic chiasm, giving off the optic nerves, is situated 

 anteriorly in the narrow median portion of the middle cranial fossa. Further posteriorly, the 

 hypophysis cerebri is imbedded in the sella turcica. 



