THE CEREBRUM 459 



lateral ventricles through the foramen interventriculare (O.T. 

 foramen df Monro). 



The cerebrum is connected with the parts in the posterior 

 cranial cavity (pons, cerebellum, and medulla oblongata) by 

 a narrow stalk called the mid-brain, or mesencephalon. The 

 mid-brain is built up of a ventral portion, the pedunculi 

 cerebri, passing between the pons and the cerebrum (Fig. 

 185, a), and a dorsal portion, the lamina quadrigemina. 

 It is tunnelled by a narrow passage the aquceductus cerebri 

 (O.T. aqueduct of Sylvius) which connects the fourth and 

 the third ventricles. 



THE CEREBRUM. 



Cerebral Hemispheres. Each cerebral hemisphere presents 

 a lateral, a medial, and an inferior surface, which are separated 

 from one another by more or less distinctly marked borders. 

 The lateral surface is convex, and is adapted to the concavity 

 of the cranial vault. The medial surface is flat and perpen- 

 dicular, and is more or less completely separated from the 

 corresponding surface of the opposite hemisphere by the falx 

 cerebri, which occupies the longitudinal fissure. The inferior 

 surface is irregular, and is adapted to the anterior and middle 

 cranial fossae, and also to the upper surface of the tentorium 

 cerebelli. Traversing this surface, in a transverse direction, 

 nearer the anterior than the posterior end of the hemisphere, 

 is the stem of the lateral fissure (O.T. Sylvian) (Fig. 182). 

 This deep cleft divides the inferior surface into an anterior 

 or orbital area, which rests upon the orbital plate of the frontal 

 bone and is, consequently, concave from side to side, and a 

 more extensive posterior or tentorial area, which lies on the 

 floor of the lateral part of the middle cranial fossa and the 

 upper surface of the tentorium cerebelli. The tentorial 

 portion of the inferior surface is arched antero- posteriorly, 

 and looks medially as well as downwards. 



The borders which separate the surfaces from each 

 other are the supero-medial, the superciliary, the infero- 

 lateral, the medial occipital, and the medial orbital. The 

 supero-medial border, convex antero-posteriorly, intervenes 

 between the medial and lateral surfaces. The superciliary 

 border is highly arched, it separates the orbital surface 



