1488 A MANUAL OF ANATOMY 



tensor tympani muscle by means of a branch from the otic ganglion ; 

 and (4) the tensor palati muscle, through the otic ganglion. 



Sixth or Abducent Nerve. — The fibres of this nerve arise from the 

 abducent nucleus, which is situated in the dorsal part of the pons 

 Varolii, close to the median line. It lies above the striae acusticag 

 on the floor of the fourth ventricle, subjacent to the eminentia 

 teres. The fibres emerge from the inner part of the nucleus, and 

 pass through the lower part of the pons in a forward and 

 slightly downward and outward direction to the point where the 

 nerve makes its superficial appearance, namely, the lower border 

 of the pons, just external to the pyramid of the medulla oblongata. 



The abducent nucleus receives collaterals from the dorsal or 

 posterior longitudinal bundle, and a functional connection is thereby 

 established between that nucleus and the oculo-motor nucleus. 

 The internal rectus muscle of one side and the external rectus of 

 the other side are thus associated muscles. 



The sixth nerve supplies the external rectus muscle of the eyeball. 



Seventh or Facial Nerve. — The facial nerve is composed of two 

 parts. One of these consists of efferent or motor fibres, and is 

 known as the facial nerve proper. The other part, of small size, 

 consists of afferent or sensory fibres, and is called the pars inter- 

 media of Wrisberg. The facial nerve proper arises from the facial 

 nucleus, which is situated deeply in the dorsal part of the lower 

 portion of the pons Varolii. The fibres of the nerve pursue an 

 intricate course before appearing superficially. They at first pass 

 backwards and inwards to the floor of the fourth ventricle. Here 

 they turn upwards, lying close to the median line in the form of a 

 single bundle. The nerve then makes a sharp bend outwards, and 

 passes forwards through the pons in a downward and outward 

 direction to its place of emergence. In its course within the 

 pons the nerve is intimately related to the dorsal aspect of the 

 abducent nucleus. 



The intrapontine part of the facial nerve proper is intimately 

 related to the following structures : 



1. The abducent nucleus. 4. The spinal root of the fifth 



2. The superior olive. nerve. 



3. The corpus trapezoides. 5. The dorsal or posterior 



longitudinal bundle. 



The motor facial nucleus receives fibres from the following 

 sources: (i) The corpus trapezoides, being thereby brought into 

 connection with the cochlear division of the auditory nerve ; (2) the 

 spinal root of the fifth cranial or trigeminal nerve, which is the 

 sensory nerve of the face ; and (3) the pyramidal tract of the opposite 

 side, being thereby brought into connection with the pre-Rolandic 

 motor area of the cerebral cortex. 



All the foregoing fibres terminate within the nucleus in arboriza- 

 tions around its component cells. 



