410 PRACTICAL ANATOMY. 



2. Explain internal and external branches of the posterior divisions of the spinal 

 nerves. 



The internal branches are small, and supply the sixth and seventh groups of 

 muscles and the skin on each side of the spine for an inch or two inches. The 

 external branches supply all the other proper muscles of the back and the 

 remainder of the skin. All the thirty-one pairs of posterior divisions of spinal 

 nerves divide as previously indicated, except the first. This is called the suboccipital 

 nerve. 



3. Define what is meant by proper muscles of the back. 



All those muscles not acting on the shoulder girdle ; those under the verte- 

 bral aponeurosis. 



4. Give a description of the superficial fascia of the back. 



It is very thick and dense, and contains granular fat. Abscesses often form 

 here. A favorite place for carbuncles is in the superficial fascia of the neck. 



5. Name the muscles of the back not supplied principally by t/te posterior divi- 

 sions of the spinal nerves. 



The trapezius, the latissimus dorsi, the levator anguli scapulae, and the rhom- 

 boids, major and minor. 



SHORT SUMMARY OF THE CRANIAL NERVES. 



How are the cranial nerves classified ? 



According to the new classification of cranial nerves there are twelve pairs, 

 enumerated serially from before backward, from the olfactory, or first, to the 

 hypoglossal, or twelfth, inclusive. This classification was proposed by Soemmer- 

 ing in 1778. Prior to this time the classification of Willis had been in use for 

 more than a century, by which classification only ten pairs were recognized. 



Make a further distinction between the classifications of the cranial nerves by 

 Soemmering and Willis. 



In the seventh pair Willis included both the facial, a nerve of motion, and 

 the auditory, a nerve of the special sense of hearing. The eighth pair of Willis 

 included the ninth, tenth, and eleventh nerves of our classification. The ninth 

 pair of Willis included the hypoglossal, and the tenth pair of Willis included the 

 first cervical, called the suboccipital nerve. 



What is understood by superficial and deep origins of cranial nerves f 



By the former is meant the place where the nerve is seen attached to the 

 surface of the brain (Fig. 92) ; by the latter is meant the place deeply located, 

 called a nucleus of gray matter, to which the motor part of nerves can be traced. 



Docs not the sensory part of nerves also have a deep origin .' 



Properly speaking, the sensory parts of nerves have their origin in the cells 

 of the posterior root ganglia of the nerve-trunks, to which ganglia special atten- 

 tion must be given in the dissection of both cranial and spinal nerves. The 

 sensory fibres originating in the ganglia grow inward to this nuclei, and, as far 

 as is known, form there no direct connection with the nerve-cells. 



Is there any correspondence between the origins of the cranial nerves and the 

 origins of the spinal nerves ? 



Yes ; each has a superficial and a deep origin. The superficial origin of the spinal 

 nerves is readily seen on removing the spinal cord from its neural canal. The 

 deep origin of the spinal nerves is from the anterior and posterior horns of the 

 gray crescents of the interior horns of the spinal cord. 



What further resemblance between cranial and spinal nerves may be mentioned / 



(i) Fibres from the deep origin of each pass upward and are connected with 

 the cortex of the cerebrum ; (2) the pneumogastric nerve arises by motor and 

 sensory roots from nuclei which are derivatives of the anterior and posterior 



