CRURA CEREBRI. 131 



-_ f Phrenic, distributed to the diaphragm. 



| Intercostals, distributed to the intercostal muscles. 

 r . r f , -j Facial nerve, or portio dura, to the facial muscles. 

 Centntuga External branch of spinal accessory, to the trapezius 



erves. an( j s t e rno-cleido-mastoid muscles. 



PONS VAROLII. 



The Pons Varolii unites together the cerebrum above, the cerebellum 

 behind, and the medulla oblongata below. It consists of transverse and 

 longitudinal fibres, amidst which are irregularly scattered collections of gray 

 or vesicular nervous matter. 



The transverse fibres unite the two lateral halves of the cerebellum. 



The longfaidinal fibres are continuous (i) with the anterior pyramids 

 of the medulla oblongata, which interlacing with the deep layers of the 

 transverse fibres, ascend to the crura cerebri, forming their superficial or 

 fasciculated portions; (2) with fibres derived from the olivary fasciculus, 

 some of which pass to the tubercula quadrigemina, while others, uniting 

 with fibres from the lateral and posterior columns of the medulla, ascend 

 in the deep or posterior portions of the crura cerebri. 



Properties and Functions. The superficial portion is insensible and 

 inexcitable to direct irritation ; the deeper portion appear to be excitable, 

 consisting of descending motor fibres ; the posterior portions are sensible but 

 inexcitable to irritation. 



Transmits motor impulses and sensory impressions from and to the 

 cerebrum. 



The gray ganglionic matter consists of centres which convert impressions 

 into conscious sensations, and originate motor impulses, these taking place 

 independent of any intellectual process; they are the seat of instinctive 

 reflex acts; the centres which assist in the coordination of the automatic 

 movements of station and progression. 



CRURA CEREBRI. 



The Crura Cerebri are largely composed of the longitudinal fibres of 

 the pons (anterior pyramids, fasciculi teretes) ; after emerging from the pons 

 they increase in size, and become separated into two portions by a layer of 

 dark gray matter, the locus niger. 



The superficial portion, the crusta, composed of the anterior pyramids, 

 constitute the motor tract, which terminates, for the most part, in the corpus 



