AVES. 81 



SPINAL CORD. The spinal cord in the swan is continued from the oblong 

 medulla ; it passes down of nearly the same size ; about the middle of the neck it is 

 rather smaller, and at the lower part begins to increase, and becomes still larger about 

 the middle of the portion, giving off the nerves to the axillary plexus ; it then 

 gradually diminishes, and a great part of the thoracic portion continues of nearly the 

 same size as the upper part of the cervical ; towards the loins it increases again, and 

 becomes most enlarged about the middle of the portion, giving off the nerves to the 

 lower extremities. A little above and below this part, there is a separation of the two 

 posterior halves of the cord at the ventricle, which is covered only by membrane ; the 

 spinal cord begins to diminish again, and becomes gradually less as it approaches 

 the extremity of the tail. In the dorsal and lumbar portions, where no motion is 

 allowed, the cord fills the spinal canal, and in many parts is covered closely by a thin 

 plate of vitreous bone. The anterior and posterior bundles of each nerve are of nearly 

 the same size ; and in one of the largest nerves, the anterior bundle could not be so 

 clearly separated from the ganglion as in man, neither in the turtle. 



SPINAL NERVES. The number of the cervical nerves is various in different 

 species, each of them is divided into an anterior and posterior trunk ; the anterior is 

 given to the muscles and skin, and the posterior principally to the muscles; but 

 generally the three inferior and first dorsal form the axillary plexus. In the swan the 

 two preceding cervical nerves communicate together, and then with the first entering 

 the plexus, and are distributed on the muscles at the posterior part of the scapula, 

 corresponding with the trapezius, the levator of the scapula, and rhomboid, and on the 

 skin. Several branches from the plexus are given to the pectoral muscles, and that 

 resembling the great serrated. The circumflex nerve passes from the spiral ; it gives 

 a branch to a muscle analogous to the broadest muscle of the back, and is then 

 distributed on the deltoid. The internal cutaneous passes from the trunk, giving off 

 the median and ulnar, and descends at the inner side of the humerus to the skin. The 

 spiral nerve gives branches to the teres and scapular muscles ; it sends branches to the 

 internal brachial muscle, and the extensor corresponding with the triceps : in passing 

 behind the fore-arm it gives a branch to supply the skin ; at the back of the ulnar it 



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