476 A MANUAL OF VETERINARY PHYSIOLOGY 



enter the restiform body which forms the posterior peduncle of 

 the cerebellum, and so gain access to the cerebellum. Some 

 of these arcuate fibres enter the restiform body on its own side. 

 The restiform body is formed from the direct cerebellar tract of 

 the cord. The fibres of this tract terminate in the median 

 hemisphere, or vermis, of the cerebellum by arborising around 

 the Purkinje cells of the body. Other fibres connect the medulla 

 with the cerebellum, for fibres pass from the olivary body through 

 the restiform body of the opposite side to the cerebellum. 



|Such, briefly, is the arrangement of the bulb. It is better for 

 the purpose of description to continue carrying the sections 

 forward both through the pons and mid-brain. 



The Pons lies between the bulb and the cerebral peduncles. If 

 a section be made through it, the appearance presented does not 

 differ materially from that furnished by a section of the upper 

 extremity of the medulla, with the exception that bundles of 

 fibres taking a transverse course are passing to the middle 

 peduncles of the cerebellum. Between these fibres is the grey 

 matter, or nuclei pontis. From the dorsal surface of the pons 

 is formed the anterior cerebellar peduncles. Fibres course 

 through the pons from one side of the cerebellum to the other, 

 and from the cerebrum to the pons. The pyramidal fibres 

 reach into the pons, and are spoken of as the cortico-pontine. 

 Though the fibres are described as reaching into the pons from 

 the pyramid, it will be remembered the flow is in the opposite 

 direction, and that these fibres are passing from the cerebral 

 cortex backwards into the cord. In this section can be seen the 

 nucleus of Deiters, a collection of large multipolar cells, in the 

 floor of the fourth ventricle, which is intimately connected with 

 afferent and efferent mechanisms, and is one of the cell-ter- 

 minations of the vestibular branch of the eighth nerve. From 

 the pons arise the important fifth pair of cranial nerves. 



A section through the Mid- Brain shows that the reticular 

 structure of the pons is continued forward ; it is enlarged by 

 fibres derived from the opposite cerebellar cortex, and fibres 

 from the nuclei of the fifth and eighth cranial nerves. The 

 nervous mass formed by these structures bifurcates into the 

 crura cerebri, or cerebral peduncles, and these constitute the ventral 

 portion of the mid-brain. Each peduncle is divided by a groove 

 into two portions — a dorsal, known as the tegmentum, and a 

 ventral, or crusta. Between the two is a collection of grey 

 matter known as the substantia nigra. In the crusta the motor, 

 and in the tegmentum the sensory fibres are contained ; it 

 therefore constitutes an important highway between the cerebrum 

 and the body. 



Functions of the Bulb. — We have seen that this is the path by 



