54 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



1 1. Spinal Recurrent. — So called because, arising from 

 the spinal cord outside of the cranium, it passes upward 

 within the backbone, enters the skull, and again comes 

 out to be distributed to the muscles of the shoulder. It 

 is a motor nerve. 



12. Hypoglossal. — Arising from the medulla, low 

 down, just before it becomes the cord, it passes out to 

 be distributed to the tongue and to become its motor 

 nerve. It therefore controls articulation. 



General Obseivations on Cranial Nerves. — Observe (i) 

 they all except No. i come from the base of the brain 

 or intercranial continuation of the axis; (2) all except 

 1 and 2 come from the medulla ; (3) all the special 

 senses are to be found here; (4) in most cases the sen- 

 sory and motor fibers are embodied in separate nerves, 

 in this regard differing from the spinal nerves, which 

 have each two roots, a sensory and a motor. 



Spinal Nerves. — As already said, there are of these 

 thirty-one pairs, each with its two roots. Their dis- 

 tinctive functions are not so different as in the case of 

 the cranial, and they do not therefore need distinct 

 names. They are divided into four groups : cervical, 

 dorsal, lumbar, and sacral. There are eight cervical, 

 twelve dorsal, five lumbar, and six sacral. Those of each 

 group are numbered first, second, third, etc. (Fig. 35). 



Distribution. — Most of these are distributed to adja- 

 cent parts of the body, but in the upper and lower por- 

 tion of the series several are united to form the great 

 limb nerves. Thus the fifth, sixth, seventh, and eighth 

 cervical and first dorsal form a plexus from which go the 

 nerves of the arm and hand, while the two last lumbars 

 and four of the sacrals form the plexus from which go 

 the great nerves which supply the leg and foot. In all 

 cases by division and subdivision the branches become 

 smaller and smaller until they pass beyond the power 



