342 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



Make a diagram through the cord showing its funiculi and the roots of the 

 spinal nerves. 



Make a clean cut across the cord and examine the cut surface. The section 

 is divisible into a central darker material, the gray matter, shaped like a butter- 

 fly, in which the nerve cells of the cord are located; and a much thicker white 

 material, the white matter, surrounding the gray matter and composed of nerve 

 fibers. The white matter is subdivisible into the funiculi named above. Each 

 funiculus consists of a number of tracts or bundles of fibers whose functions are 

 known, but these tracts are not visibly differentiated from each other. 



3. The peripheral distribution of the posterior cranial nerves. — In this 

 section will be described the peripheral course of the fifth, seventh, and ninth to 

 twelfth cranial nerves. For the complete dissection of these, it is necessary to 

 have a specimen of which the head is intact, but most of them can be found, in 

 part at least, on the same specimen on which the previous dissections were made. 



a) The eleventh or spinal accessory nerve: This nerve supplies the sterno- 

 mastoid, cleidomastoid, levator scapulae ventralis, and trapezius muscles. It is 

 a pure motor nerve and is apparently derived from the vagus. 



Rabbit: Separate the sternomastoid and cleidomastoid on the one hand 

 from the basioclavicularis and levator scapulae ventralis on the other. Running 

 near the dorsal border of the levator scapulae ventralis and parallel to it is the 

 spinal accessory nerve. Branches of the second to fourth spinal nerves pass 

 ventral to it and unite with it by branches. Trace it posteriorly and note its 

 branches on the inner surface of the trapezius. Trace it anteriorly and note 

 branches to the levator scapulae ventralis, sternomastoid, and cleidomastoid. 



Cat: Cut through the clavotrapezius near its origin and deflect it ventrally, 

 thus exposing the levator scapulae ventralis. On the inner surface of the clavo- 

 trapezius along the dorsal border of the levator scapulae ventralis runs the main 

 part of the spinal accessory nerve. Trace it posteriorly, noting branches into 

 the trapezius muscles and the levator scapulae ventralis. Trace it anteriorly. 

 It passes dorsal to the second cervical nerve to which it is corfnected by a net- 

 work, and near this region gives branches to the sternomastoid and cleidomastoid 

 muscles. It then passes through the cleidomastoid muscle. 



b) The vagus, the sympathetic, and the hypoglossal nerves: Follow the vagus 

 and sympathetic anteriorly. Stretch the head forward by cutting across the 

 lateral muscles of the neck. At about the level of the posterior end of the larynx 

 the vagus and carotid artery are crossed ventrally by the descending branch of the 

 hypoglossal or twelfth cranial nerve. This passes obliquely caudad toward 

 the median line and supplies the sternohyoid, sternothyroid, and thyrohyoid 

 muscles. Continue forward. At about the place where the common carotid 

 artery divides into external and internal carotids a conspicuous nerve is seen 

 crossing the ventral surface of the vagus and carotid artery and curving ante- 

 riorly. This is the main part of the hypoglossal nerve. Follow it forward. It 



