Fig. 9. Frontal Section through the Crus Cerebri at the level of the 

 Posterior Corpora Quadrigemina. 



The Mesencephalon (Crura) containing all the Projection Fibres from the 

 Cerebral Hemispheres is divided into 2 layers, an upper the "tegmentum", a lower 

 the "crusta" ; these are separated by the "substantia nigra". The Tegmentum chiefly 

 contains: — 



1. Fibres from Thalamus and Corpora Quadrigemina. To these belongs 

 the so-called posterior commissure which represents the connection of 

 the Tegmen with the Thalamus of the opposite side. 



2. Fibres from Lenticular Nucleus. Cf. Explanation to Fig. 8. 



3. Fibres from Cortex. To these belongs the path of "Muscle-Sense". 

 Cf. Text to Fig. 7. It moreover contains 3 Nuclei. 



a) Nucleus of Descending Root of Vth Nerve on either side of the 

 Aqueduct of SYLVIUS. 



b) Nucleus of the Ilird (Oculomotor) Nerve, on either side of the Aque- 

 duct of Sylvius. 



c) Nucleus of the IV th Nerve which lies posterior to the Ilird Nucleus 

 at the posterior end of the Aqueduct of SYLVIUS. 



The Internal Geniculate Body probably belongs to the auditory path. 

 The posterior longitudinal bundle is derived partly from the anterior column of 

 the spinal cord and possibly connects the nuclei of the motor nerves of the eye. 



A large number of the fibres in the tegmentum stop in the "Red Nucleus" 

 where new fibres arise to cross the middle line and leave the tegmentum by 

 passing to the Cerebellum through the Superior Cerebellar Peduncle. (Cf. Fig. 6 Text.) 



The Crusta chiefly contains: — 



1. Cortico-crustal Fibres — Geniculate Bundle (Meynert). 



2. Frontal Cortico-pontic Tract which passes from the Frontal Lobe and 

 Caudate Nucleus to the Pontine Nuclei, whence fibres cross the middle 

 line and pass to the Cerebellum through the Middle Cerebellar Peduncle. 



3. Pyramidal Tracts. Cf. Fig. 7 Text. 



4. Qccipito-temporal cortico-pontic Tract which passes from the Temporal 

 and Occipital lobes to the Pontine Nuclei. Course of these fibres as in 2. 



The course and function of the fibres in close proximit}' to the Sub- 

 stantia Nigra is unknown. 



Fig. 10. Convolutions of the Brain and Sutures of the Skull 



in the New-Born. 



The detailed description of the convolutions is given in the text accom- 

 panying the following figures. We only desire to lay stress upon, the high position 

 of the Fissure of SYLVIUS, and the Fontanelles. 



The smaller fontanelles (Sphenoidal and Mastoid) may be very small at 

 birth; whereas the largest, the Frontal, remains open till the end of the first 

 year of life. 



