LEPUS CUNICULUS 



335 



The hypoglossal nerve is a stout trunk that comes out of the 

 skull by the condylar foramen and runs backwards lateral to the 

 preceding nerves and slightly inwards. When it reaches a point 

 near the place where the common carotid artery splits into its 

 internal and external branches it divides into two. The anterior 

 nerve crosses the internal carotid artery ventrally and runs forward 

 parallel to and outside the external carotid, and also to the posterior 

 cornu of the hyoid bone to the base of the tongue, which it serves 

 together with the muscles of that region. The posterior branch 

 passes backwards, and after a short distance crosses the common 

 carotid ventrally and breaks up into branches supplying the muscles 

 of the hyoid and thyroid region. Some of these nerves receive fibres 

 also from the first and second spinal nerves. 



Spinal Cord. 



The spinal cord passes back without visible line of de- 

 marcation from the hinder end of the medulla oblongata as a 



FIG. 114. Roots of a spinal nerve issuing from the cord. From Quain. 

 A, from before ; B, from the side ; C, from above ; D, the roots separated. 



i ventral fissure ; 2, dorsal fissure ; 3 and 4, lateral grooves of the cord ; 5 ventral root 

 6 posterior root ; 6', dorsal ganglion ; 7, the united or compound nerve ; 7 , the dorsal 

 branch. In A one ventral root is divided and turned upwards. 



long rod, at first somewhat oval, but soon nearly round, the whole 

 length of the neural canal. The side walls of the posterior end of the 

 roof of the fourth ventricle meet together in the mid-dorsal line, 



